JPH10340450A - Disk surface test device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a disk surface test device which can detect existence of extremely small ruggedness on a disk surface. SOLUTION: An optical section 13 irradiates a disk surface with a laser beam through a movable object lens 11, and receives its reflected light by a quadruple photodiode and a CCD. An image read out by the CCD is stored in an image storing section 14, the image is processed by a ruggedness detecting section 16, and existence of minute ruggedness on a disk surface. An automatic focus control section 18 detects a distance from an object lens to a disk surface by an astigmatic method based on a RF signal 20 from and a FOCUS signal 21 from the quadruple photodiode, and generates a lens driving signal 22 based on the distance. Preferably, an object lens position is concentrated within a position detection range by an astigmatic method using a position detecting element (PSD) which can detect a wider detection rang than a position detection range by an astigmatic method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a disk surface inspection apparatus for inspecting the surface of a disk such as a magnetic disk or a semiconductor wafer.

[0002]

2. Description of the Related Art In a magnetic disk used for a hard disk drive, a magnetic head normally floats slightly above the surface to write and read data. Therefore, if there are irregularities on the disk surface, particularly projections, the magnetic head collides with the projections, causing damage or malfunction.

[0003] Therefore, no such projection must exist on the disk surface. Therefore, it is necessary to inspect the surface of the magnetic disk before being incorporated in the apparatus, and to exclude a disk having undesirable irregularities.

FIG. 19 shows the principle of a conventional magnetic disk surface inspection apparatus. This is the rotating disk 191
The tip of the needle 193 attached to the tip of the arm 194 is brought into contact with the surface of the arm 194, and the vibration of the tip of the needle 193 is converted into an electric signal by the piezoelectric element 195 attached to the arm 194, and based on this electric signal, To detect the unevenness state 192 of the disk surface.

Japanese Patent Application Laid-Open No. 62-235511 discloses an apparatus for inspecting the state of the disk surface in a non-contact manner using a laser beam instead of the contact type. This detects the reflected light from the disk surface,
For each predetermined section of the disk, a statistic expressing the state of the surface in the section is obtained, and the surface state of the disk is inspected based on the statistic. As the reflected light detecting means, a semiconductor light spot position detector having a continuous light receiving surface is used.

[0006]

By the way, for example, Nikkei Electronics No. 1997.3.10 (No. 68)
4) As described in pp 141-151, the flying height of the head has become extremely small (for example, about 25 μm) in order to increase the density of magnetic recording. As a result, even the protrusions on the disk surface of a size that has not been a problem in the past have become a problem.

In the above-mentioned contact-type inspection apparatus, it is physically impossible to detect the above minute unevenness due to its mechanical structure.

In the inspection apparatus described in Japanese Patent Application Laid-Open No. 62-235511, the surface condition is determined based on statistics obtained from light reflected from the disk surface. It is not possible to detect individual minute projections or the like. Further, in order to detect minute projections and the like using such a light beam, the surface deflection d2 due to the rotation of the disk and the thickness d of the disk as shown in FIG.
The presence of one error (for example, several hundred μm) is also a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and has as its object to provide a disk surface inspection apparatus capable of detecting the presence or absence of extremely small irregularities on the disk surface. It is in.

Another object of the present invention is to provide a disk surface inspection apparatus capable of accurately detecting the presence or absence of extremely small irregularities on the disk surface despite the presence of surface runout and disk thickness errors due to disk rotation. Is to provide.

[0011]

A disk surface inspection apparatus according to the present invention is a disk surface inspection apparatus for detecting the presence or absence of minute irregularities on the surface of a disk to be inspected.
A light beam generator for generating a light beam to be irradiated onto the disk surface, a movable objective lens for focusing the light beam generated by the light beam generator on the disk surface, and a movable control for movably controlling the objective lens An optical unit that includes a control unit and reads an image on the disk surface, an image storage unit that stores an image read by the optical unit as an image, and an image storage unit that processes the image stored in the image storage unit to process the image on the disk surface. Image processing means for detecting the presence or absence of minute irregularities, and detecting the distance from the objective lens to the disk surface based on a signal obtained from the objective lens of the optical unit, and changing the position of the objective lens based on the distance. Automatic focus control means for performing focus control.

The inventor of the present invention uses an interference optical system that utilizes the coherence of a light beam having a coherent property such as a laser beam to detect minimal unevenness on the disk surface through image processing. did. At that time, the focal position of the light beam irradiated portion on the disk surface of the light beam needs to be adjusted within the depth of focus of the objective lens. On the other hand, the disc has a thickness error and also has a surface runout due to the rotation of the disc, so that the focal position is shifted. Therefore, in the present invention, for such a relatively large fluctuation of the surface position (for example, 1 μm or more), the focus state is automatically obtained by adjusting the position of the objective lens by the automatic focus control means. That is, the disk surface position fluctuation and the disk thickness error are dealt with using the automatic focus control means, and then minute irregularities on the disk surface are detected by image (light interference image) processing.

[0013] Thus, the very small unevenness of the magnetic disk for high-density recording having a very small head flying height.
It is possible to accurately detect each individual.

The image processing means preferably detects the presence / absence of minute irregularities based on an interference image generated by a change in the optical path length of a light beam applied to the disk surface due to the minute irregularities on the disk surface. Is what you do.

The optical section has, for example, a four-divided photodetector for receiving a spot image of a light beam applied to the surface of the disk, and the automatic focus control means controls the automatic focus control based on the output of the four-divided photodetector. Performs distance detection by the astigmatism method,
Automatic focus control is performed on the objective lens based on the detected distance.

Alternatively, the optical section has a pair of photodetectors located at different distances from the objective lens for receiving a spot image of a light beam applied to a disk surface,
The automatic focus control means performs distance detection by a differential concentric circle method based on the outputs of the pair of photodetectors, and performs automatic focus control on the objective lens based on the detected distance.

By combining the above-described configuration of the present invention, that is, combining the interference optical system and the astigmatism optical system (or the differential concentric optical system), the spot system (beam waist) of the light beam on the disk surface can be widened. It becomes possible to do. If, for example, it is intended to improve the accuracy of detecting unevenness using only the astigmatism optical system, it is necessary to reduce the size of the spot system. Thereby, it is possible to detect even a smaller portion by enlarging the uneven portion with a lens. However, if it is enlarged too much, the range of the part to be observed becomes narrow. Because, in the astigmatism method, P
This is because only a spot can be observed because there is only a function to detect only D. Therefore, it is necessary to reduce the spot diameter, that is, the beam waist, in order to perform highly accurate detection.

On the other hand, in the present invention, by utilizing the interference optical system, the role of the astigmatism optical system is changed from the detection of unevenness to the objective of focus control such that the objective lens only needs to be focused to some extent. Can be changed to This eliminates the need for the astigmatism optical system to have a function of detecting minute irregularities, so that the portion to be observed can be made wider. Further, since the interference optical system can detect minute unevenness in a wide range, there is no problem even if the beam waist is wide. However, the interference becomes undetectable when a certain focus error (usually several tens of μm) occurs. Therefore, by controlling the objective lens by an astigmatism method or the like and setting the focus error within the error range, the height is reduced. A wider range of measurements can be made in the direction.

More preferably, the optical section has lens position detecting means for detecting a lens position in a range larger than the range of the distance detected by the distance detection, and the automatic focus control means firstly sets the lens The position of the objective lens is driven into the narrower range of the distance detection according to the detection result by the position detection means, and then the automatic focus control of the objective lens is performed based on the detected distance. This makes it possible to cope with a larger disc surface position fluctuation in the automatic focus control.

The optical section has, for example, a one-dimensional sensor arranged in a radial direction of the disk and scanned spirally or concentrically with respect to the disk, and the image storage section includes the one-dimensional sensor. The image data is stored based on the signal obtained by the photoelectric conversion. Thereby, coupled with the widening of the beam waist, the inspection can be performed with a relatively wide band-like width along the circumferential direction of the disk,
Inspection time can be reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. Hereinafter, the surface inspection of a magnetic disk will be described. However, the present invention is not limited to the magnetic disk, and can be applied to the surface inspection of any medium that needs to detect minute irregularities on the disk surface. For example, it can be used for surface inspection of a semiconductor wafer.

First, FIG. 1 shows a configuration of a main part of a magnetic disk surface inspection apparatus according to an embodiment of the present invention.

The disk surface inspection apparatus 100 includes a spindle motor 19 for rotating the magnetic disk 10 to be inspected, and an optical unit 13 for irradiating the disk surface of the magnetic disk 10 with a light beam and receiving reflected light from the disk surface. And an image storage unit 14 which receives the CCD image signal 12 output from the optical unit 13 and stores it as an image.
An unevenness detecting unit (image processing means) 16 for processing the image signal 15 stored in the image storage unit 14 to detect the presence or absence of minute unevenness on the disk surface;
An automatic focus control unit 18 for performing automatic focus adjustment of No. 3 is provided.

At the time of inspection of the magnetic disk 10, the magnetic disk 10 is driven to rotate at a predetermined rotational speed by a spindle motor 19, the optical unit 13 has a movable objective lens 11, and the automatic focus control unit 18 In response to an RF signal 20 and a FOCUS signal 21 described below,
The lens driving signal 22 is output to the optical unit 13.

FIG. 18 shows the appearance of a magnetic disk to be inspected in this embodiment. The magnetic disk 10 has a so-called texture that is intentionally flawed for floating the head, which is conventionally provided on the entire surface of the disk for high-density recording, only on the disk outer peripheral portion 187, and the inner peripheral portion 186 has a so-called texture. Mirror surface without texture. In the example of the figure, three protrusions 188 are illustrated as a defect as a defect of the magnetic disk.

FIG. 13 shows the disk surface inspection apparatus 10.
0 is connected to a LAN 139 via a personal computer (PC) 138. By connecting a plurality of such sets of the disk surface inspection apparatus 100 and the PC 138 to the LAN 139, it is possible to inspect a plurality of disks at the same time.

In the disk surface inspection apparatus 100 shown in FIG. 13, in addition to the configuration of the main part shown in FIG.
4 shows a mechanism for rotating the magnetic disk and sliding the optical unit / processing unit 130, which are controlled by the PC 138. The optical unit / processing unit 130 includes the optical unit 13, the image storage unit 14, the unevenness detection unit 16, and the automatic focus control unit 18 in FIG.
Is equivalent to

The magnetic disk 10 is driven to rotate by the spindle motor 19 through the spindle controller 131 under the control of the PC 138 as described above. This rotation operation is detected by the encoder 132, and the detection signal
138. Thus, the PC 138 can recognize the current rotation angle θ of the magnetic disk with respect to the optical unit 13. On the other hand, the optical unit 13 is a PC 138
The magnetic disk 10 is slid in the radial direction by the slide motor 136 via the slide control unit 135 under the control of. This slide operation is detected by the circle coder 137, and the slide position information r is returned to the PC 138. Therefore, the PC 138 can recognize the position on the disk surface to be inspected based on r and θ, and can associate this with the detected position of the uneven portion. Although not shown, the PC 138 can display on the disk surface where the irregularities are detected based on the information.

As a result of the rotation of the magnetic disk 10 and the sliding of the optical unit 13, the light beam emitted from the optical unit 13 is scanned spirally or concentrically on the disk surface relative to the magnetic disk 10. . Therefore, a band-like image along the circumferential direction of the disk surface can be obtained. This strip preferably overlaps with the adjacent strip. This is to prevent the irregularities at the boundary of the band from being overlooked.
The spiral or concentric circle is determined by whether the slide is performed intermittently or continuously. In the present embodiment, the disk surface is inspected spirally from the outer circumference to the inner circumference of the disk.

Although not shown, these devices are installed in a clean room, and all processes from transport of the magnetic disk to mounting and inspection are automatically performed. The PC 138 has an optical unit
In addition to the detection signal 17 from the processing unit 130, a serial number (SN) recorded on each magnetic disk 10 is read and sent to the PC 138. As shown in FIG. 14, the PC 138 stores the serial number (Disk No.) of the magnetic disk processed by itself, the serial number (SN), and the number of errors (the number of irregularities detected) of the disk.
As described above, since the band to be detected overlaps with the adjacent band, the same concavo-convex portion may be detected in duplicate, but may be the same based on the aforementioned information on r and θ. Since it can be understood, the number of the uneven portions is counted as one.

A host computer is connected to the LAN 139, and the PC 138 responds to the request from the host computer or voluntarily outputs this inspection result to the P.
Send to C138.

Next, the principle of the laser interference and the principle of the astigmatism method employed in this embodiment will be described with reference to FIG. In the present embodiment, minute irregularities on the disk surface are detected by performing image processing on an interference image of light read from the disk surface. On the other hand, when the disc surface position fluctuation is larger than this, the fluctuation is detected by the astigmatism method, and the focus control of the optical unit 13 is performed based on the detection result.

FIG. 2A shows the principle of laser interference. A laser diode (L
D) The coherent light beam generated from 31 is split in two directions by the beam splitter 32 toward the disk 10 and the fixed mirror (reference glass) 34, and the reflected lights of the two merge at the beam splitter 32. have a finger in the pie. This interference light is transmitted to the CCD image sensor 3 as a sensor.
5 is detected. In the present embodiment, the CCD image pickup device 3
5 constitutes a one-dimensional sensor composed of 4096 pixels. While the distance between the beam splitter 32 and the mirror 34 is fixed, if the distance between the beam splitter 32 and the disk surface changes, the interference light changes in brightness.
Therefore, interference fringes are generated in the two-dimensional image of the disk surface according to the unevenness of the disk surface. By analyzing the interference fringes by image processing described later, minute (for example, about several nm) irregularities can be detected.

FIG. 2B illustrates the principle of the astigmatism method. This is because the light beam from the laser diode 31 is reflected by the beam splitter 32 toward the disk 10, and the light reflected on the disk surface is reflected by the cylindrical lens (CL) 3.
A configuration is adopted in which the light enters the four-division photodiode (PD) 37 through the photodiode 6. Regarding the astigmatism method, the configuration and operation of the four-divided PD 37 will be further described with reference to FIGS.

FIG. 3A shows the structure of the four-divided PD 37. The quadrant PD 37 has photodetectors A, B, C, and D divided into four equal areas. On the 4-split PD 37,
An image of the spot of the illuminated light beam is formed on the disk surface. The shape of this image is shown in FIGS.
As shown in FIG. 5, the spot shapes S1, S2, S as shown in the drawing correspond to the distance from the objective lens 11 to the disk surface, ie, to “close”, “focal position”, “far”
3 is known to change. Therefore, the sum A + B + C + D obtained by adding all the outputs of the photodetectors A, B, C, and D
Is obtained as a reflection (RF) signal, and the difference (A + B) − (C + D) of the sum of the diagonal photodetectors is obtained as a focus (FOCUS) signal. (Each photodetector A,
Outputs of B, C, and D are represented as A, B, C, and D, respectively. FIG. 4 shows the relationship between the voltage values of the RF signal and the FOCUS signal and the distance from the objective lens 11 to the disk surface.
As can be seen from the figure, the RF signal shows a peak at the focus position, and the output decreases as the distance from the focus position increases or decreases. On the other hand, the output value of the FOCUS signal is
An intermediate value 0 is shown at the focal position, and the sign of the output is reversed depending on whether the focal position is approaching or moving away from the focal position, and changes in proportion to the change in distance. And the output value of the FOCUS signal is
When it exceeds the detection range of the distance, it rapidly decreases. Therefore, based on the output values of both signals, it is determined whether the relative distance between the objective lens 11 and the disk surface is at the focal position, and in any direction to reach the focal position when the relative distance between the objective lens 11 and the disk surface is deviated. It can be recognized whether the objective lens 11 should be moved.

Next, FIG. 5 shows a specific example of the configuration of the optical unit 13. This incorporates both the laser interference and astigmatism configurations described with reference to FIGS. 2A and 2B. In this embodiment, the laser diode 31 emits a laser having a wavelength of 670 nm. The laser beam output from the laser diode 31 is converted into parallel light by the collimating lens 30, and is converted into a mirror 34 by the beam splitter 32.
And the objective lens 11 in two directions. Objective lens 1
The laser beam directed to 1 is reflected on the surface of the magnetic disk 10, passes through the objective lens 11 again, passes through the beam splitter 32, and goes to another beam splitter 33.
On the other hand, the laser beam reflected by the mirror 34 is reflected by the beam splitter 32 toward the other beam splitter 33. These two reflected laser beams are
Further, the beam is split by the beam splitter 33 in two directions. One of the divided parts is directed to the CCD image sensor 35 via the intermediate lens 39, where an image of the interfering light (interference image) is detected. The other is a cylindrical lens 36 and an intermediate lens 3
Then, the light is directed to the four-divided PD 37 via 8, and the light spot image described above is formed thereon. The cylindrical lens 36 has a function of generating critical aberration, and the intermediate lens 38 has a function of focusing on the PD 37. The objective lens 11 is movably supported by a lens driving unit 60 described later. In FIG. 5, all parts except the objective lens 11 and the magnetic disk 10 are fixed.

Hereinafter, a specific configuration of the main elements shown in FIG. 1 will be described.

FIG. 6 shows the structure of the lens driving section 60 of the optical section 13. The objective lens 11 is a magnetic shield case 6
1 is movably supported in the optical axis direction via a lens damper 66. A drive coil 65 is fixed to the objective lens 11. The drive coil 65 is located in the space formed by the magnetic members 64 and 68 forming the P pole and the N pole in contact with the magnet 63. A lens cover 67 is provided to prevent dust from entering the case 61. In addition,
FIG. 6 also shows a position detecting element 62 used in a second embodiment described later. The position detection element 62 detects the position of the objective lens 11 in the vertical direction.
It is an element like SD (Position Sensitive Diode),
It is fixed to the inner wall of the case 61.

With respect to the lens driving unit 60, the optical unit 1
The distance from the objective lens 11 to the disk surface is detected based on the signal obtained from the third objective lens 11, and a lens drive signal 22 (FIG. 1) generated according to the detected signal.
Through the drive coil 65, the position of the objective lens 11 in the optical axis direction is controlled.

FIG. 7 shows a schematic configuration of the inside of the image storage unit 14. The image storage unit 14 includes an A / D converter 71 that receives the image signal 12 from the CCD imaging device 35 of the optical unit 13 and converts the image signal 12 into a digital signal, a memory 72 in which the digital signal is written, and a memory 72. And a read / write control unit 73 for controlling writing and reading of the data. In the present embodiment, the CCD image sensor 35
The one-dimensional images taken in are read out in series, sequentially converted into corresponding digital signals, and written to the memory 72. The memory 72 reproduces a two-dimensional image by arranging one-dimensional images in parallel.

In this image, bright and dark interference fringes appear as shown in FIG. 8 by employing the laser interference described above. This image is analyzed by image processing by the unevenness detecting unit 16 and the presence of the minute unevenness portion 81 is detected. The unevenness detection unit 16 uses a digital signal processor (DSP),
The uneven portion can be detected by a known method.

FIG. 9 shows a second embodiment obtained by improving the above embodiment.
3 shows a schematic configuration of automatic focus control according to the embodiment. In the second embodiment, not only the RF signal 20 and the FOCUS signal 21 are obtained from the astigmatism distance detection unit 91 using the above-described four-divided PD 37, but also the position detection of the lens driving unit 60 described with reference to FIG. Position detection (P
SD) A signal 94 is obtained. The automatic focus control unit 93 receives these signals 20, 21 and 94, determines the current lens position, generates a lens drive signal 22 that can obtain an appropriate in-focus state, and outputs this to the lens drive unit. Supply to 60.

First, the significance of the second embodiment will be described with reference to FIG.
This will be described below.

FIG. 10A shows the value (vertical axis) of the PSD signal 94 of the position detecting element 62 with respect to the absolute position (horizontal axis) of the objective lens 11. FIG. 10B shows the relative position of the objective lens 11 with respect to the disk surface, that is, the value of the FOCUS signal 21 (vertical axis) with respect to the distance between them (horizontal axis).
As can be seen from FIG. 10B, normally, the distance detection range of the astigmatism method is limited to a relatively narrow range of ± 5 μm (10 μm). This is because the detection range cannot be expanded in order to make the position control accuracy of the objective lens 11 as high as ± 500 nm. Therefore, if the objective lens 11 deviates from this distance detection range, it is difficult to perform normal automatic focus control. Therefore, in this embodiment,
By providing the position detecting element 62 described above, the position of the objective lens 11 can be detected in a wider range, for example, in a distance detection range of ± 500 μm (1000 μm).

The automatic focus control unit 93 (FIG. 9) performs control based on the PSD signal 94 so that the current position of the objective lens 11 falls within the astigmatism detection range. After entering, the position of the objective lens 11 is controlled based on the FOCUS signal 21 so as to achieve a more appropriate focusing state.

As shown in FIG. 15, the position detecting element 62 includes a light emitting element 153 and a light receiving element 154, and a light blocking member 151 for transmitting the movement of the objective lens 11 is inserted between the light emitting element 153 and the light receiving element 154. With this configuration, the position of the objective lens 11 is detected in a relatively wide detection range as described above according to the amount of light received by the light receiving element 154. However, the positional accuracy itself is about ± 10 μm, which is not so high.

When the distance detection by the astigmatism method is sufficient by employing a high-precision drive mechanism or the like, the PSD signal (accordingly, the position detection element 62) and the control based thereon are unnecessary.

FIG. 11 shows a specific configuration example of the automatic focus control unit 93 according to the second embodiment. PSD in the figure
If the signal is set to a predetermined fixed value, it can be used as the automatic focus control unit 18 in the first embodiment. Also,
In the first embodiment, P
Elements related to the SD signal (such as the A / D converter 112) may be excluded.

FIG. 11 shows an A / D converter 111, which receives an RF signal, a PSD signal, and a FOCUS signal, respectively.
112, 113, adaptive control unit 116, DEFECT filter 114, PID control unit 115, phase control unit 11
7, an oversampling filter 118 and a D / A converter 119. "IIR type" in the figure is Infi
This shows a digital filter of the nite Impulse Response type.
This configuration can be configured by an existing digital signal processor.

The DEFECT filter 114 is a digital filter for removing the influence of the texture on the outer periphery from the reflected signal on the disk surface and detecting large irregularities. As a result, it is possible to prevent the automatic focus control from becoming unstable in a large uneven portion (larger than the texture and not including the disk thickness and the disk surface deflection). That is, for example, if there are scratches (irregularities) of several hundred μm or more, the control of the objective lens 11 by the astigmatism method cannot follow these irregularities, and the servo may be deviated. Therefore, in such a case, the control of the objective lens 11 is intentionally stopped, and the objective lens is stopped at the same position until the uneven portion passes. Then, the control is restarted after the irregularities are excessively removed.

The PID control unit 115 is a digital filter that executes various processes such as proportional, integral, and derivative. The phase control unit 117 is a digital filter for correcting a response characteristic of the lens driving unit 60. The oversampling filter 118 is a low-pass filter for cutting a frequency component higher than the response characteristic of the lens driving unit 60. Also, it works as a filter for preventing an excessive response due to the phase control. The adaptive control unit 116 is a unit for monitoring signals from various units to optimize various control states such as servo AGC.

FIG. 12 is a flowchart showing an example of a specific procedure of the DSP control of the automatic focus control unit 93 in FIG. First, the RF signal, PSD signal, and FOCUS
The signal is read from the A / D converters 111, 112, 113 (S121). Next, a DEFECT filter is executed (S122). Next, the PID control unit 115, the phase control unit 117, and the oversampling filter 11
8 are executed (S123). continue,
The control output signal output from the oversampling filter 118 is output to the D / A converter 119 (S12).
4). Then, adaptive control (S1) is performed by the adaptive control unit 116.
After performing step 25), the process returns to step S121, and the above processing is repeated.

In the adaptive control, for the next cycle, the RF signal read in step S121 is used, and PSD control (position sensor control) is performed or FOCUS control (FIG. 10 ( b)). In the PSD control, only the portion beyond the detection range of the FOCUS control is controlled, and the objective lens 11 is moved to a position detection range in which the FOCUS control can be performed. F
In the OCUS control, the coefficients of each IIR filter are determined based on the signal level of the servo AGC within the narrow position detection range so that the signal is not distorted.

As described above, the astigmatism method is used for detecting a relatively narrow relative lens position, but another method may be used. FIG. 16 shows the principle diagram. This is called a differential concentric circle method, and the beam widths D1 and D1 at positions 161 and 162 at different distances from the objective lens 10 are described.
The difference between the two quantities is detected by a photodetector, and the sum and difference of the two are calculated.

FIG. 17 shows a specific arrangement of elements corresponding to FIG. Elements similar to those in FIG. 5 are given the same reference numerals. One output of the beam splitter 33 is directed to the CCD image pickup device 35 as in the case of FIG. 5, but the other output is split into two by the other beam splitter 177 via the intermediate lens 176, and is directed to PD 171 and PD 172. The arrangement positions of both PDs 171 and 172 are equivalently arranged at positions 161 and 162 in FIG. The sum of the outputs of both PDs is obtained by the adder 173, and this signal becomes the RF signal. The difference between the outputs of the two PDs is obtained by the subtractor 174, and this signal becomes the FOCUS signal.

In the astigmatism method, it is sufficient to dispose a PD at one location, so that space can be saved. On the other hand, the differential concentric circle method does not require the use of a 4-split PD, so that the cost of the apparatus can be reduced.

[0057]

As described above, according to the disk surface inspection apparatus of the present invention, the presence / absence of extremely small irregularities on the disk surface can be detected. Further, it is possible to accurately detect the presence / absence of extremely small irregularities on the disk surface regardless of the presence of surface runout and disk thickness error due to disk rotation. Further, since the beam waist of the light beam can be widened, the disk surface can be inspected in a strip shape, and the inspection time required can be reduced.

[0058]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a magnetic disk surface inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of laser interference (a) and the principle of astigmatism method (b) employed in the present embodiment.

FIG. 3 is a diagram illustrating the configuration and operation of a four-segment PD.

FIG. 4 is a graph showing a relationship between a voltage value of an RF signal and a FOCUS signal and a distance from an objective lens to a disk surface.

FIG. 5 is a configuration diagram illustrating a specific configuration example of the optical unit illustrated in FIG. 1;

FIG. 6 is a schematic sectional view showing a structure of a lens driving unit of the optical unit shown in FIG.

FIG. 7 is a block diagram illustrating a schematic configuration inside an image storage unit illustrated in FIG. 1;

8 is an explanatory diagram of an image showing bright and dark interference fringes stored in a memory 72 of FIG. 7;

FIG. 9 is a block diagram illustrating a schematic configuration of an automatic focus control according to a second embodiment of the present invention.

FIG. 10 shows an objective lens 2 according to the second embodiment.
6 is a graph showing two position detection ranges.

FIG. 11 is a circuit block diagram illustrating a configuration example of an automatic focus control unit according to the second (first) embodiment.

FIG. 12 is a flowchart illustrating a control example of an automatic focus control unit in FIG. 11;

FIG. 13 shows a disk surface inspection apparatus of FIG.
FIG. 2 is a configuration diagram showing a system configuration connected to a LAN via C).

FIG. 14 is an explanatory diagram showing an example of inspection result data stored in the PC of FIG.

15 is a configuration diagram showing a specific configuration example of the position detection element shown in FIG.

FIG. 16 is a principle diagram of a differential concentric circle method instead of an astigmatism method for detecting a relative lens position.

FIG. 17 is an explanatory diagram showing a specific element arrangement for the differential concentric circle method of FIG. 16;

FIG. 18 is an external view showing an external appearance of a magnetic disk to be inspected in the embodiment of the present invention.

FIG. 19 is a principle view of a conventional magnetic disk surface inspection apparatus.

[Explanation of symbols]

10 magnetic disk, 11 objective lens, 12 CCD
Image signal, 13 optical unit, 14 image storage unit, 15 image signal, 16 unevenness detection unit, 17 detection signal, 18 automatic focus control unit, 19 spindle motor, 20 RF signal, 21 FOCUS Signal, 22... Lens drive signal, 3
DESCRIPTION OF SYMBOLS 1 ... Laser diode (LD), 32, 33 ... Beam splitter, 34 ... Mirror, 35 ... CCD image sensor, 36
... Cylindrical lens, 37 ... Division photodiode (P
D), 38, 39: intermediate lens, 60: lens driving unit,
61: Magnetic shield case, 62: Position detecting element (PS
D), 63: magnet, 64: magnetic member, 65: drive coil, 66: lens damper, 67: lens cover, 68:
Magnetic member, 93: automatic focus control unit, 94: PSD signal, 132: encoder, 136: slide motor, 1
37 ... encoder, 138 ... PC, 139 ... LAN.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01N 21/88 G01N 21/88 G

Claims (6)

[Claims] 1. A disk surface inspection apparatus for detecting the presence or absence of minute irregularities on the surface of a disk to be inspected, comprising: a light beam generator for generating a light beam to be irradiated on the disk surface; A movable objective lens for focusing the light beam generated by the optical disc on the disk surface, and a movable control unit for movably controlling the objective lens, an optical unit that reads an image on the disk surface, and an optical unit that is read by the optical unit. An image storage unit that stores the image as an image, an image processing unit that detects the presence or absence of minute irregularities on the disk surface by processing the image stored in the image storage unit, and an objective lens of the optical unit. Focus control is performed by detecting the distance from the objective lens to the disk surface based on the obtained signal and changing the position of the objective lens based on the distance. And an automatic focus control means. 2. The image processing means detects the presence or absence of minute irregularities based on an interference image generated by a change in the optical path length of a light beam applied to the disk surface due to the minute irregularities on the disk surface. 2. The disk surface inspection apparatus according to claim 1, wherein: 3. The optical section has a four-divided photodetector for receiving a spot image of a light beam applied to the surface of the disk, and the automatic focus control means performs non-focus based on an output of the four-divided photodetector. 3. The disk surface inspection apparatus according to claim 1, wherein a distance is detected by a point aberration method, and automatic focus control is performed on the objective lens based on the detected distance. 4. The optical section has a pair of photodetectors located at different distances from the objective lens for receiving a spot image of a light beam applied to a disk surface, and the automatic focus control means includes: The distance detection according to a differential concentric circle method is performed based on outputs of the pair of photodetectors, and automatic focus control is performed on the objective lens based on the detected distance. Disk surface inspection equipment. 5. The optical section has lens position detecting means for detecting a lens position in a range larger than the range of the distance detected by the distance detection, and the automatic focus control means firstly detects the lens position. The position of the objective lens is driven into a narrower range of the distance detection according to a detection result by the means, and then automatic focusing control of the objective lens is performed based on the detected distance. A disk surface inspection apparatus according to any one of claims 1 to 4. 6. The optical unit has a one-dimensional sensor arranged in a radial direction of the disk and scanned spirally or concentrically with respect to the disk.
The disk surface inspection apparatus according to claim 1, wherein image data is stored based on a signal photoelectrically converted by the one-dimensional sensor.