JPH09269363A - Magnetic defect inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable measuring of magnetic characteristics of a generation area with non-contact and non-destruction by collecting polarized laser light, irradiating a magnetic field disk applying a magnetic field therewith, detecting to analyze the polarized state of reflection light and identifying an error generation position. SOLUTION: A beam 2 from a laser light source 1 is made linearly polarized collected light beam via a beam expander 3, a polarizer 4, a prism 5 and a lens 6 and made incident on a magnetic disk 7. Reflection beam corresponding to a car rotation angle reversely goes to enter a detector 9 by the magnetic film of the disk 7. Signals are written and read on the magnetic disk 7 with a magnetic head 13 every prescribed track to detect errors, their generation addresses are matched to a laser spot position and they are regulated. A horizontal magnetic field of about two times holding force of the disk 7 generated in a magnetic field generation means 10 is regulated until the car rotation angle is the maximum, and an optical signal is detected to generate the optical magnetic field hysteresis loop of the generation address. The loop out of the generation address is made and the magnetic characteristics of the generation address is identified from their comparison.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk defect inspection apparatus, and more particularly to a magnetic defect inspection apparatus suitable for inspecting and measuring a fine magnetic defect of a thin film magnetic disk.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for miniaturization and increased capacity of magnetic storage devices, and the magnetic disks used for this have been miniaturized and the 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 capable of such high-density recording, errors in writing and reading signals tend to increase with the increase in density, and the defect area occupying the recording area per bit that causes an error is small. Therefore, the maximum defect area that can be tolerated is 3-4 μm in diameter, which approximates a circle for a 5 GB level magnetic disk.
A 10 GB level magnetic disk is expected to have a diameter of 2 to 3 μm. 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. Although these defects may be visually observable, they cause the above-mentioned errors.
It is usually difficult to visually observe with a maximum defect area of 2 to 4 μm in diameter. Conventionally, identification of an error occurrence position (defect occurrence position) of a magnetic disk is performed by, for example, "HEWLETT-PA.
An error tester for magnetic disks is used, as detailed in CKARD JOURNAL ", November, 1985. That is, the strength of a signal read by the same or a different magnetic head from the signal written by the magnetic head. The measurement is performed to detect a bit whose intensity is out of a predetermined range as an error.In general, this type of tester is a device that can determine the bit position from the recording track position and the reference point. Therefore, it is possible to assign the address of the error occurrence position.By the way, the reduction of defects of the magnetic disk is an important problem in manufacturing a high recording density magnetic disk, and in order to solve this,
First of all, it is possible to accurately and accurately know the defect occurrence position on the magnetic disk, and then to analyze this by making full use of analytical means such as microscope observation and scanning electron microscope observation, and to improve the manufacturing process. is necessary. However, no consideration has been given to these points in the above-mentioned conventional technology. As general documents of this type of technology, the latest magnetic recording technology and device / equipment editing committee edition: latest magnetic recording technology and device / equipment, published in 1984 by General Publishing.

[0003]

The above-mentioned prior art has the following problems. That is, (1) Even if the error address can be assigned, if the magnetic disk is removed from the tester to observe the status of the error position, the smaller the defect area that causes the error, the more difficult it is to find it. (2) For the above reason, even if a defective portion such as a shape abnormality is confirmed at the error bit generation position, if the magnetic characteristics of the recording film at this portion cannot be measured, the shape abnormality or the like causes the error. There are problems such as that it cannot be determined, and (3) if the magnetic recording film has characteristic deterioration even if there is no abnormality in appearance under microscope observation, it is virtually impossible to confirm and observe the error position. is there.

An object of the present invention is to solve the above problems in the prior art, to accurately identify the error occurrence position of the magnetic disk, and to accurately determine the magnetic characteristics of the error occurrence area at the level of the recorded bit area. Another object of the present invention is to provide a magnetic defect inspection apparatus for a longitudinal recording magnetic disk capable of non-contact and non-destructive measurement.

[0005]

The above object is achieved by combining a magnetic disk error tester with a vertical Kerr effect measuring device having magnetic field generating means capable of sweeping a magnetic field in the horizontal direction. 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 horizontal magnetic field, the intensity of the light changes with a hysteresis characteristic with respect to the sweep magnetic field, resulting in V
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 an ordinary magnetic characteristic evaluation means such as SM (Vibrating Sample Magnetometer). Thereby, the coercive force (Hc) and the squareness ratio (S
*) Can be measured accurately. Since this gives information only on the area irradiated by the polarized laser light, by arranging an optical means for focusing the polarized laser light on the bit area level and condensing it, the magnetic characteristics of the minute area can be contacted,
Non-destructive measurement becomes possible. In order to realize a miniaturized irradiation area, a normal incidence vertical Kerr effect measuring device is adopted by adopting a normal incidence optical system using a triangular prism in place of a normal oblique incidence optical system. According to this method, the irradiation diameter of the laser beam on the magnetic surface can be changed by selecting the wavelength of the laser light source and the numerical aperture NA (Numerical Aperture) of the objective lens. For example, He-N with a wavelength of 633 nm
By combining the e-laser light and the objective lens with NA of 0.63, the laser irradiation diameter becomes 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.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an optical system diagram of this embodiment and a side view of the main part of the apparatus. 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 becomes a minute polarized beam according to the Kerr rotation angle due to the magnetic film of the magnetic disk 7, goes backward, passes through the objective lens 6, is reflected by the triangular prism 5, passes through the analyzer 8, and is the detector. Guided to 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. A combination of a He-Ne laser with a wavelength of 633 nm and an objective lens with an NA of 0.63 results in a laser beam aperture diameter of about 1 μm. The magnetic disk 7 is an air spindle 11 which can be linearly moved by a pulse motor 12 on a surface plate 15.
It is fixed so as to rotate integrally with the air spindle 11. The air spindle 11 enables addressing on the magnetic disk 7. The magnetic head 13 for writing and reading a recording signal is the base block 1
4 is fixed. 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. Next, a signal is written for each track at a predetermined recording frequency and a recording current, and then read out, and if it is out of a predetermined read output intensity range, for example, it is measured as a missing pulse or an extra pulse error.
Then, 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 area generated on the magnetic disk can be measured with non-contact and non-destructive and with high position accuracy. Moreover, since the laser spot diameter is narrowed down to about 1 μm level, a 1-bit error occurs. Even if there is, the magnetic characteristics within this bit area can be identified, and a high-resolution, high-accuracy defect inspection apparatus can be provided to suppress or reduce the increase in errors that accompanies the higher recording density of magnetic disks. . 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 1 μm.
Although the present invention is not limited to this, the laser spot diameter can be further reduced by using, for example, a laser light source having a shorter wavelength and an objective lens having a larger NA. Yes, performance is improved.

[0007]

As described above, according to the present invention,
The polarized laser light is applied to the measurement target micro area, and the information of the reflected laser light is processed optically and electrically, so the magnetic characteristics of the micro area are non-contact,
It is possible to realize a magnetic defect inspection apparatus which is non-destructive and can be measured with high accuracy, and which is particularly applied during the manufacturing process of a magnetic disk and greatly contributes to the improvement of the process.

[Brief description of drawings]

FIG. 1 is an optical system diagram of a magnetic defect inspection device exemplified in an embodiment of the present invention and a schematic diagram showing a configuration of a main part of the device.

[Explanation of Codes] 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

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[Procedure amendment]

[Submission date] November 27, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Magnetic defect inspection method

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk defect inspection method , and more particularly to a magnetic defect inspection method suitable for inspecting and measuring fine magnetic defects of a thin film magnetic disk.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for miniaturization and increased capacity of magnetic storage devices, and the magnetic disks used for this have been miniaturized and the 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
Level magnetic disk approximates a circle with a diameter of 3-4μ
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. As general documents of this type of technology, the latest magnetic recording technology and device / equipment editing committee edition: latest magnetic recording technology and device / equipment, published in 1984 by General Publishing.

[0003]

The above-mentioned prior art has the following problems. That is, (1) Even if the error address can be assigned, if the magnetic disk is removed from the tester to observe the status of the error position, the smaller the defect area that causes the error, the more difficult it is to find it. (2) For the above reason, even if a defective portion such as a shape abnormality is confirmed at the error bit generation position, if the magnetic characteristics of the recording film at this portion cannot be measured, the shape abnormality or the like causes the error. There are problems such as that it cannot be determined, and (3) if the magnetic recording film has characteristic deterioration even if there is no abnormality in appearance under microscope observation, it is virtually impossible to confirm and observe the error position. 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.

[0005]

SUMMARY OF THE INVENTION The above object, a magnetic disk
Magnetic defect inspection to inspect and measure magnetic defects at minute positions
The magnetic disk is removed from the rotating shaft.
The recording frequency and recording voltage at the specified recording frequency.
Write a signal for each predetermined track and then read
And, if it goes out of the specified read output intensity range, an error will occur.
Detecting and recording the address information of the error occurrence position
Then, stop the movement of the magnetic disk and
Adjust so that the error occurrence address is at the laser spot position.
And the pre-adjusted laser beam
The laser spot irradiates the address where the error occurred
And the magnetic field generating means.
Of water twice the coercive force of the magnetic disk generated by
The horizontal magnetic field is adjusted until the Kerr rotation angle is maximized.
A stage that detects the signal and detects the magnetic characteristics of the error occurrence address
Floors and optical magnetic field hiss located outside the above error occurrence address
Measure the loop and measure the magneto-optical property at the above error occurrence address.
Error occurrence number compared with the field hysteresis loop
Magnetic defects including at least the step of identifying magnetic properties of the earth
This is achieved by adopting an inspection method . That is, when the surface of the magnetic material is irradiated with laser light polarized by the polarizer,
As is well known, the plane of polarization rotates (Kerr effect) due to optical-magnetic interaction, which can be observed as the intensity of light through an analyzer. 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 sweep magnetic field, and as a result, VSM (Vibrating Sample Magnet).
It is possible to obtain an optical-magnetic field hysteresis loop corresponding to a BH (magnetic flux density vs. magnetizing force) hysteresis loop obtained by a usual magnetic characteristic evaluation means such as a tometer. 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 on the area irradiated by the polarized laser light, by arranging an optical means for focusing the polarized laser light on the bit area level and condensing it, the magnetic characteristics of the minute area can be contacted, Non-destructive measurement becomes possible. Adopting a normal incidence optical system that uses a triangular prism instead of the normal oblique incidence optical system to realize a smaller irradiation area
Then, the wavelength of the laser light source and the numerical aperture NA of the objective lens
By selecting (Numerical Aperture), the irradiation diameter of the laser beam on the magnetic surface can be changed. For example, by combining He-Ne laser light with a wavelength of 633 nm and an objective lens with NA of 0.63, the laser irradiation diameter becomes 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.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the magnetic defect inspection method of the present invention .
It is an optical system diagram used for the method, and a side view of the main part of an apparatus.
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. Next, a signal is written at a predetermined recording frequency and a predetermined recording current for each predetermined track, and then read out. When the signal is out of a predetermined read output intensity range, for example, a missing pulse or an extra pulse error is measured, and a track N
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 area generated on the magnetic disk can be measured with non-contact and non-destructive and with high position accuracy. Moreover, since the laser spot diameter is narrowed down to about 1 μm level, a 1-bit error occurs. Even if there is, the magnetic characteristics within this bit area can be identified, and a high-resolution, high-accuracy defect inspection method can be provided to suppress or reduce the increase in errors due to the increase in recording density of magnetic disks. . 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,
It is possible to realize a magnetic defect inspection method which is non-destructive and can be measured with high accuracy, and which is particularly applied during the manufacturing process of a magnetic disk and greatly contributes to the improvement of the process.

[Brief description of drawings]

FIG. 1 of the present invention 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.

[Explanation of Codes] 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)

[Claims] 1. A magnetic defect inspection apparatus for inspecting and measuring a magnetic defect at a minute position on a magnetic disk, which collects polarized laser light and irradiates the magnetic disk vertically to detect the polarization state of the reflected laser light. And a polarization detecting means, a magnetic field generating means for applying a magnetic field to the magnetic disk, a positioning means for linearly and rotationally moving the magnetic disk to position the magnetic disk at an arbitrary position, and a function for writing / reading a signal to / from the magnetic disk. A magnetic defect inspection apparatus comprising: an error analysis unit having a function of measuring a signal error and displaying an error address.