JP2793990B2 - Magnetic defect inspection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a defect inspection method for a magnetic disk, and more particularly to a method suitable for inspecting and measuring minute magnetic defects on a thin film magnetic disk. The present invention relates to a magnetic defect inspection method . 2. Description of the Related Art In recent years, magnetic storage devices have been increasingly required to be smaller and have larger capacities, and magnetic disks used therein have been reduced in size and recording density has been increased. For example, a magnetic disk of the current maximum capacity of 5 GB (gigabyte) level has a surface recording density of about 14 Mbit / i.
nch ² [mega bits / (inch) ² ], and the recording area per bit is about 60 μm ² (2.5 μm × 23 μm).
It has become. Further, in the case of a 10 GB level magnetic disk, the areal recording density becomes about 29 Mbit / inch ² ,
The recording area per bit is also about 25 μm ² (1.6 μm × 16
μm). In a magnetic disk that enables such high-density recording, errors in signal writing and reading tend to increase with the increase in density, and the defect area occupying a recording area per bit that causes an error is also small. And the maximum allowable defect area is 5 GB
For a level magnetic disk, the diameter is approximately 3 to 4μ approximating a circle.
m, 10 GB level magnetic disk with a diameter of 2-3 μm
It is expected. Defects that cause errors in the magnetic disk mainly include missing magnetic films, local deterioration of magnetic film characteristics, and geometrical abnormalities on the surface such as scratches, protrusions, and contamination. These defects can be visually observed in some cases, but it is usually difficult to visually observe the maximum defect area having a diameter of 2 to 4 μm, which causes the above-described error. Conventionally, an error occurrence position (defect occurrence position) of a magnetic disk is identified by, for example, “HEWLETT”.
-PACKARD JOURNAL ", November, 19
As detailed in 1985, a magnetic disk error tester is used. That is, the strength of a signal written by a magnetic head and read by a same or different magnetic head is measured, and a bit whose strength is out of a predetermined range is detected as an error. Normally, this type of tester is a device that can determine the bit position of the recording track position and the bit position from the reference point, so that the error occurrence position can be assigned. By the way, the reduction of defects in a magnetic disk is an important problem in the manufacture of a high-density magnetic disk. To solve this problem, it is necessary to first know the location of defects on a magnetic disk accurately and accurately. In addition, it is necessary to make use of analytical means such as microscopic observation and scanning electron microscope observation to analyze the results and to improve the manufacturing process. However, no consideration has been given to these points in the above-mentioned conventional technology. General literature on this type of technology includes the latest technology of magnetic recording and the latest edition of magnetic recording and editing by the Editing Committee for Devices and Equipment, published by 1984 in General Publishing. [0003] The above prior art has the following problems. (1) Even if the address of the error can be assigned, if the magnetic disk is removed from the tester for observing the situation of the error position, the smaller the defect area causing the error becomes, the more difficult it is to find it. (2) For the above reason, even if a defect such as a shape abnormality is found at the position where an error bit occurs, if the magnetic characteristics of the recording film in this part cannot be measured, the shape abnormality or the like may cause an error. (3) Even if there is no apparent abnormality in microscopic observation etc., if the magnetic recording film has characteristic deterioration, it is practically impossible to confirm and observe the error position, etc. is there. An object of the present invention is to solve the above-mentioned problems in the prior art, accurately identify an error occurrence position on a magnetic disk, and accurately determine the magnetic characteristics of an error occurrence area at the level of a recorded bit area. Non-contact, non-destructive measurement An object of the present invention is to provide a magnetic defect inspection method for a magnetic disk. An object of the present invention is to provide a magnetic defect inspection method for inspecting and measuring a magnetic defect at a minute position on a magnetic disk, wherein the magnetic disk is mounted without being removed from a rotating shaft. state, write signal for each track in a predetermined recording frequency, recording current, then reads,
If the error is outside the predetermined read output intensity range, the error is detected as an error, the address information of the error occurrence position is recorded, and the movement of the magnetic disk is stopped once , and the laser spot of the laser light where the error occurrence address is polarized. And adjusting the laser beam to come to the position, and irradiating the previously adjusted laser beam to the error occurrence address, and performing focusing so that the laser spot has a minimum diameter,
Adjusting the horizontal magnetic field of about twice the coercive force of the magnetic disk generated by the magnetic field generating means until the Kerr rotation angle is maximized, detecting the optical signal, and detecting the magnetic characteristics of the error occurrence address; Measuring the optical magnetic field hysteresis loop at a position deviating from the error occurrence address and comparing it relatively with the optical magnetic field hysteresis loop at the error occurrence address,
This is achieved by a magnetic defect inspection method that includes at least a step of identifying a magnetic characteristic at an address where an error occurs. In other words, when a laser beam polarized by a polarizer is applied to the surface of a magnetic material, as is well known, the plane of polarization is rotated by photo-magnetic interaction (Kerr effect). It can be observed as the intensity of light. At this time, by sweeping the magnetic field in the horizontal direction, the intensity of the light changes with a hysteresis characteristic with respect to the swept magnetic field. As a result, VSM (Vibrating Sa) is obtained.
It is possible to obtain a light-magnetic field hysteresis loop corresponding to a BH (magnetic flux density vs. magnetizing force) hysteresis loop obtained by ordinary magnetic property evaluation means such as a simple magnetometer. Thereby, the coercive force (Hc) and the squareness ratio (S *), which are the basic characteristics of the magnetic recording film, can be accurately measured. Since this gives information only in the region irradiated by the polarized laser light, by arranging optical means for focusing and condensing the polarized laser light to the bit area level,
It becomes possible to measure the magnetic properties of a micro area in a non-contact, non-destructive manner. If a normal incidence optical system using a triangular prism is adopted in place of the normal oblique incidence optical system in order to realize the miniaturization of the irradiation area, the wavelength of the laser light source and the numerical aperture NA (Numerical Aperture) of the objective lens can be obtained. By selecting, it is possible to change the laser beam irradiation diameter on the magnetic body surface. For example, a He-Ne laser beam having a wavelength of 633 nm,
By combining with an objective lens with NA of 0.63,
The laser irradiation diameter is about 1 μm. Therefore, by irradiating the address identified by the error test with the polarized laser light, the magnetic characteristics of the error region can be inspected and evaluated in a non-contact and non-destructive manner. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an optical system diagram and a side view of a main part of the apparatus used in the magnetic defect inspection method of the present invention.
In FIG. 1, reference numeral 1 denotes a laser light source such as a semiconductor laser or a He-Ne laser. A laser beam 2 emitted from a laser light source 1 is converted into a parallel light beam by a beam expander 3, converted to a linearly polarized light beam by a polarizer 4, reflected by a triangular prism 5 to become vertically incident light, and condensed by an objective lens 6. Irradiated on the magnetic disk 7. The irradiated polarized beam is converted into a minute polarized beam corresponding to the Kerr rotation angle by the magnetic film of the magnetic disk 7, passes backward through the objective lens 6, is reflected by the triangular prism 5, and is reflected by the analyzer 8.
And is guided to the detector 9. By selecting the wavelength of the laser beam and the NA of the objective lens 6, the beam diameter on the surface of the magnetic film can be narrowed down. 633nm wavelength
The combination of the He-Ne laser described above and an objective lens having an NA of 0.63 results in a laser beam stop diameter of about 1 μm. The magnetic disk 7 is mounted on an air spindle 11 that can be linearly moved by a pulse motor 12 on a surface plate 15.
1 so as to rotate integrally therewith. The air spindle 11 enables addressing on the magnetic disk 7. A magnetic head 13 for writing and reading a recording signal is fixed to a base block 14. Below the laser beam spot, a Weiss-type magnetic field generator 10 for applying a horizontal magnetic field is provided. The polarizer 4 and the analyzer 8 are desirably Glan-Thompson prisms because of the extinction ratio and ease of optical axis adjustment, and the triangular prism 5 is desirably a Berek prism. Next, a measurement procedure according to the present embodiment will be described. (1) First, the magnetic disk 7 is fixed on the air spindle 11, and the air spindle 11 is linearly moved by the pulse motor 12 until the magnetic head 13 is positioned on the magnetic disk 7. By rotating the air spindle 11, the magnetic head 13 flies above the magnetic disk 7. Then, a predetermined recording frequency, the write signals for each track by the recording current, then reads, Outside predetermined read output intensity range, for example, measured as missing pulse or an extra pulse error, track No.
And the error occurrence bit number or the sector number by the optical encoder 16 installed on the spindle is stored as address information (for example, r, θ) of the error occurrence position. However, the error detection system is not shown. (2) Next, the rotation of the air spindle 11 is temporarily stopped, and the spindle 11 is linearly and rotationally moved and stopped so that the error occurrence address is located at the position of the laser spot. (3) Next, a laser beam adjusted in advance is applied to an error address, and focusing is performed by a focusing mechanism (not shown) so that the laser spot has a minimum diameter. The Weiss-type magnetic field generator 10 generates a horizontal magnetic field approximately twice as large as the coercive force of the magnetic disk 7 to be measured, and sweeps the polarizer 4 and the polarizer 4 while sweeping left and right until the Kerr rotation angle is maximized. The analyzer 8 is adjusted, an optical signal is detected by a detector 9 comprising a detection system such as a photomultiplier tube, and a sweep magnetic field and a hysteresis loop of the optical signal are displayed on an XY recorder (not shown). Get the magnetic properties of the address. (4) Next, the optical-magnetic field hysteresis loop at a position deviating from the error address is measured and compared with the optical magnetic field hysteresis loop at the error occurrence address, and the coercive force, squareness ratio, and residual magnetic flux density information are determined. The amount of light to be given is identified. According to the above procedure, the magnetic characteristics of the error region generated on the magnetic disk can be measured with high accuracy in a non-contact and non-destructive manner, and the laser spot diameter is narrowed down to a level of about 1 μm. Even so, the magnetic characteristics within this bit area can be identified, and a high-resolution and high-accuracy defect inspection method for suppressing or reducing the increase in errors accompanying the increase in the recording density of the magnetic disk can be achieved. . It is needless to say that the above-described structures of the optical system and the apparatus and the measuring procedure are merely examples of the present invention. In the above embodiment, the laser spot diameter is described as being reduced to 1 μm. However, the present invention is not limited to this.
For example, a laser light source having a shorter wavelength is used, and N
By adopting a larger objective lens of A,
The laser spot diameter can be further reduced, and the performance is improved. [0007] As described above, according to the present invention,
Irradiating a laser light polarized in the measurement micro area of the test object, an optical information possessed by the reflected laser light, since it is electrically processing method, the magnetic properties of the microscopic regions noncontact,
A non-destructive and highly accurate measurement is possible, and a magnetic defect inspection method which is particularly applied during the manufacturing process of a magnetic disk and greatly contributes to the improvement of the process can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is an optical system diagram of a device used in a magnetic defect inspection method and a schematic diagram showing a configuration of a main part of the device. [Description of Signs] 1 ... Laser light source 2 ... Laser beam 3 ... Beam expander 4 ... Polarizer 5 ... Triangular prism 6 ... Objective lens 7 ... Magnetic disk 8 ... Analyzer 9 ... Detector 10 ... Weiss-type magnetic field generator 11 ... Air spindle 12 ... Pulse motor 13 ... Magnetic head 14 ... Base block 15 ... Surface plate 16 ... Optical encoder

Claims (1)

(57) [Claims] Inspecting magnetic defects of minute positions of the magnetic disk, a magnetic defect inspection method of measuring, in a state of mounting without removing the magnetic disk from the axis of rotation, a predetermined recording frequency, the signal for each track recording current And then reading it out, detecting an error when it is out of a predetermined read output intensity range, recording the address information of the error occurrence position, and temporarily stopping the movement of the magnetic disk so that the error occurrence address becomes Adjusting the laser beam to be at the position of the laser spot of the polarized laser light; and irradiating the error adjusted address with the previously adjusted laser beam, and performing focusing so that the laser spot has a minimum diameter. A horizontal magnetic field of about twice the coercive force of the magnetic disk generated by the magnetic field generating means is adjusted until the Kerr rotation angle is maximized. Adjusting the optical signal to detect the magnetic characteristic of the address where the error occurs, and measuring the optical magnetic field hysteresis loop at a position deviating from the address where the error occurs, and measuring the relative position with the optical magnetic field hysteresis loop at the address where the error occurs. A magnetic defect inspection method characterized by including at least a step of comparing magnetic characteristics and identifying a magnetic characteristic at an address where an error occurs.