JPH08304050A - Magnetic film defect inspection device for magnetic disk - Google Patents

Abstract

PURPOSE: To improve the S/N ratio of scattered light and the measurement accuracy of the crest value of a defect pulse by performing scanning by projecting a laser beam band with a proper length in the radius direction of a magnetic disk for the magnetic film of the rotating magnetic disk. CONSTITUTION: Elliptical laser beams LT outputted by a laser diode 611 become a laser beam band LB where only a short axis is reduced by a beam expander 612 to irradiate the magnetic film of a magnetic disk 1 which is rotated by a rotary mechanism 2. Reflection light LR of the magnetic film and reflection light LR' due to the defect of the magnetic film are focused by an objective lens 621 and made incident on a photodiode 622, the reflection light LR is dispersed and received by 2n (for example 24) avalanche photodiodes APD, and then each noise is outputted. Also, the scattered light LR is received by the APD corresponding to the position of a defect and a defect pulse is outputted. The difference of the output signals of two APDs in a set is calculated by a differential operation part 7 and noise due to reflection light is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection device for inspecting defects in a magnetic film of a magnetic disk.

[0002]

2. Description of the Related Art A hard magnetic disk used as a recording medium of a computer system is manufactured by applying a magnetic film on the surface of a glass substrate. If the coated magnetic film has defects such as irregularities, the recording performance is deteriorated, and therefore the presence or absence thereof is inspected by a surface defect inspection apparatus. In the present invention, this surface defect inspection apparatus is a prior art.

FIG. 4 shows the construction of this surface defect inspection apparatus, which comprises a rotating mechanism 2 for mounting and rotating a magnetic disk 1.
An inspection optical system 3 including a light projecting system 31 and a light receiving system 32, a signal processing unit 4, and a data processing unit 5. Projection system
At 31, the circular laser beam L _T oscillated by the helium neon laser oscillator tube 311 is elliptical expander 312.
Is converted into an elliptical shape by and is reflected by the mirror 313.
The magnetic film is focused on the elliptical spot S _P by the focusing lens 314 and projected onto the rotating magnetic disk 1 mounted on the rotating mechanism 2 in the direction of the incident angle θ _T of, for example, 20 ° to scan the magnetic film. The light receiving system 32 has an optical axis in the direction of a regular reflection angle θ _R equal to the incident angle θ _T of the light projecting system 31, and the spot S _P
The reflected light L _R of the magnetic film and the scattered light L _R ′ of the defect existing in the magnetic film are both condensed by the condenser lens 321, and these are divided into two by the half mirror 322.
However, since the magnetic film is not a perfectly smooth surface, its reflected light L _R contains some diffuse reflection components in addition to the specular reflection light. One of the split light beams is incident on the spatial filter 323, the reflected light L _R is almost blocked, and most of the scattered light L _R 'is transmitted and received by the photomultiplier tube (PMT) 324. The other split light is incident on the spatial filter 325, the scattered light L _R 'is substantially blocked, and most of the reflected light L _R is transmitted and received by the photodiode (PD) 326.

FIG. 5 exemplifies both output signals of the PMT 324 and the PD 326. The output signal of the PMT 324 has a noise N ₁ due to the reflected light L _R which is transmitted without being blocked by the spatial filter 323 and superposed on the noise N _1. There is a defect pulse P ₊ on the positive side with respect to the scattered light L _R ′. Also the output signal of the PD 326, and the noise N ₂ by the reflected light L _R, the negative side of the defect pulse P the intensity of the reflected light L _R is generated decreased by the same defect _- there is a, both output signals, The signal is input to the signal processing unit 4, passes through a high-pass filter, and is digitized and measured by an individually set threshold voltage. The peak value h is digitized and input to the data processing unit 5,
The coordinate position and size of the defect are calculated by the MPU 51,
These defect data are temporarily stored in the memory (MEM) 52. When the inspection of the entire surface of the magnetic disk 1 is completed, each stored defect data is appropriately edited and the printer (PR
T) 53, and the coordinate position and size of the defect are printed or displayed on a map. It should be noted that the map display has been conventionally performed in various surface inspection devices. According to this, the position where the defect exists can be clearly read, and linear defects are continuously displayed. It can be easily determined.

[0005]

Since there are subtle differences in the reflectivity of the magnetic film depending on the manufacturer and lot of the magnetic disk 1 or the position on the magnetic disk 1, the above two noises N ₁ , The level of N ₂ fluctuates, and therefore the ground level L _G also fluctuates up and down, so the threshold voltage V _S cannot be set to a constant value. On the other hand, for example, the inspection optical system 3 is separately provided with a light receiving system for measuring the ground level L _G ,
Although a method of automatically setting the threshold voltage V _S using the measured L _G has been devised, the actual situation is that an appropriate threshold voltage V _S is not always set even by such an automatic setting method. Is. Therefore, if the noise N itself due to the reflected light L _R of the magnetic film is reduced by some means, the ground level L _G becomes a voltage of "0" or close to this, and the threshold voltage V _S is unnecessary or is set. It is advantageous that both the S / N of the scattered light L _R ′ and the measurement accuracy of the crest value h of the defect pulse can be improved. The present invention has been made in view of the above, and reduces the noise N due to the reflected light L _R of the magnetic film as much as possible to bring the ground level L _G to the “0” voltage or close to this voltage and the scattered light L _R. It is an object of the present invention to provide a magnetic film defect inspection apparatus in which both the S / N of 'and the measurement accuracy of the peak value h of the defect pulse are improved.

[0006]

SUMMARY OF THE INVENTION The present invention is a magnetic film defect inspection apparatus which achieves the above-mentioned object, wherein a rotating mechanism for mounting and rotating a magnetic disk and a magnetic film of a rotating magnetic disk are provided. , A projection system for projecting and scanning a laser light band having an appropriate length in the radial direction of the magnetic disk, and a magnetic film of the laser light band provided in the direction of a regular reflection angle equal to the incident angle of the projection system. 2n avalanche photodiodes (A) provided at the image forming position of the objective lens for collecting the reflected light by the laser light and the scattered light due to the defects existing in the magnetic film and corresponding to the laser light band.
PD) is linearly arranged and has a light receiving system including a photodiode array that receives the reflected light and the scattered light that are collected. Combining suitable two of the 2n APDs, calculating the difference between the output signals of the two APDs of each combination, and eliminating the noise due to the reflected light of the magnetic film,
A difference calculation unit including n difference circuits that outputs a defect pulse for scattered light of a defect is provided.

[0007]

In the above magnetic film defect inspection apparatus, the laser beam band having an appropriate length in the radial direction of the magnetic disk is projected by the light projecting system with respect to the magnetic film of the magnetic disk mounted on the rotating mechanism and rotating. And the magnetic film is scanned and the objective lens of the light receiving system is installed in the direction of the regular reflection angle that is equal to the incident angle of the light projecting system. And the scattered light due to are collected respectively. On the other hand, a plurality of 2n APDs corresponding to the laser light band are linearly arranged in the photodiode array provided at the image forming position of the objective lens, and the reflected light collected by the objective lens is reflected by each APD. The scattered light is imaged and received on the APD corresponding to the position of the defect. The APD converts the received light into a voltage and amplifies and outputs the voltage, that is, has a good sensitivity. The 2n APDs are combined in appropriate two, and the difference between the output signals of the two APDs in each combination is calculated by the n difference circuits of the difference calculation unit, and the difference is calculated by the reflected light of the magnetic film. The noise is erased,
A defect pulse for each scattered light is output. In the above description, the reflected light of the magnetic film is dispersed and received by each APD, whereas the conventional photomultiplier tube receives all the reflected light, so that it is compared with the noise of the photomultiplier tube. , The noise per APD is reduced to 1 / n of the number of APDs, and the noise of the output signal of each two APDs is eliminated by the difference, so the scattered light of the defect is S /
N is improved, and the defect pulse is satisfactorily detected, and the peak value h thereof is also measured with good accuracy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 show an embodiment of the present invention, FIG. 1 is an overall configuration diagram of a magnetic film defect inspection apparatus, FIG. 2 is a partial view of the magnetic film defect inspection apparatus, and FIG. FIG. 3 is an operation explanatory diagram for FIG. 2. In FIG. 1, the magnetic film defect inspection apparatus has the same rotation mechanism 2, signal processing section 4 and data processing section 5 as the prior art surface defect inspection apparatus shown in FIG. An inspection optical system 6 including a 61 and a light receiving system 62, and a difference calculation unit 7 are provided and are connected as shown. The projection system 61 includes a high-intensity laser diode (LD) 611, a beam expander (EX) 612, a cylindrical lens (SYL) 613, and a mirror 614.
And the elliptical laser beam L output by LD611
_T is long and short axis is expanded by EX612, the laser beam band L _B becomes the only minor axis has been reduced by SYL613, which was reflected in the direction of the incident angle theta _T by the mirror 614, the magnetic film of the magnetic disk 1 On the other hand, the projection is performed with the major axis aligned in the radial direction. In this case, it is desirable to make the intensity distribution of the laser light band L _B as uniform as possible. The light receiving system 62 is provided at a microscope objective lens 621 and an imaging position of the objective lens 621, and a plurality of 2n are provided corresponding to the long axis of the laser light band L _B.
Avalanche photodiodes (APDs) arranged linearly in a photodiode array (APD / ARR)
Y) 622, and its optical axis is set in the direction of the regular reflection angle θ _R equal to the incident angle θ _T. Here, an example of the dimensions of the respective parts will be described. For example, the length of the major axis of the laser light band L _B is 1
mm and the magnification of the objective lens 621 is 20 times, the major axis is enlarged to 20 mm.
If the effective length of Y622 is 20 mm, it corresponds to the long axis. Note that the number 2n of APDs is, for example, 24, and these are A
It will be represented by PD _{1 to} APD ₂₄ .

FIG. 2 shows the configuration of the difference calculator 7 and the APD.
The connection system for ARRY622 is shown. Difference calculator 7
Is composed of n = 12 difference circuits DA _{1 to} DA ₁₂ , and for example, APD ₁ and APD ₁₃ of APD / ARRY 622 are:
DA ₁ is connected to the + and-input terminals of DA ₁ , respectively, and APD ₁₂ and APD ₂₄ are connected to the + and-input terminals of DA ₁₂ respectively in the order shown below, and the output sides of DA _{1 to} DA ₁₂ are It is connected to the signal processing unit 4. However, 2 APs
The combination method of D is not limited to this order, and may be any method that can effectively eliminate the noise N described below.

A method of inspecting a defect of a magnetic film will be described below with reference to FIGS. In FIG. 1, a light projecting system is attached to the magnetic film of the magnetic disk 1 mounted on the rotating mechanism 2 and rotating.
The laser light band L _B is projected by 61, and the reflected light L of the magnetic film
_R and the scattered light L _R 'due to the defect of the magnetic film are the objective lens 62.
The reflected light L _R is condensed by 1 and is incident on the APD / ARRY 622, and the reflected light L _R is dispersed and received by ₂₄ APD ₁ to APD _24, and noises N _{1 to} N ₂₄ are respectively output and scattered light L _{R. R} 'is a defect pulse p is output is received by the APD corresponding to the position of the defect. Figure 3 (a) shows APD ₁
And an example of the output signal of the APD ₁₃ is shown. The output signal of the APD ₁ has noise N ₁ whose level fluctuates temporally with the scanning of the laser beam band L _B , and the defect pulse p _a is superposed on the noise N _1. In the output signal of the APD _13, the noise N ₁₃ fluctuates in level with time, and the defect pulse p _b is superposed on it. The levels of the two noises N ₁ and N ₁₃ are approximate to each other although there may be a slight difference _if the intensity of the laser light band L _b varies. Both output signals are input to DA ₁ to calculate the difference, and the difference signal shown in (b) is output. In the difference signal, the difference between the two noises N ₁ and N ₁₃ (N ₁ −
N ₁₃ ) is almost "0" level, which is the ground level L _G, and the polarity of the defect pulse p _b is inverted while the defect pulse p _a remains unchanged. Similar differential signals are output from the respective DAs for the other two combinations of APDs. Positive and negative threshold voltages V _{S +} and V _S− close to “0” level are set in the signal processing unit 4, the differential signal is input to the signal processing unit 4, and the defect pulse p _a is changed by the threshold voltage V _{S +.} , And the defective pulse p _b is detected by the threshold voltage V _S− , and the respective peak values h _a and h _b are measured. The differential signal output from each DA is processed in the same manner, and similarly to the conventional case, the data of each peak value h is digitized and input to the data processing unit 5, and the MPU 51 calculates the coordinate position and size of the defect, These defect data are temporarily MEM
Upon completion of the inspection of the entire surface of the magnetic disk 1 stored in 52, each defect data is output to the PRT 53, and the coordinate position and size of the defect are printed or displayed as a map.

[0011]

As described above, in the magnetic film defect inspection apparatus of the present invention, the photodiode array in which a plurality of high-sensitivity APDs are arranged is used in the light receiving system, and the magnetic field condensed by the objective lens is used. The reflected light of the film is dispersed and received by each APD to reduce the noise per APD, and the scattered light of the defect existing in the magnetic film is received by the APD corresponding to the defect, and two suitable APDs are combined. By calculating the difference between the output signals of both APDs, the noise of both output signals is eliminated, the S / N of the scattered light of the defect is improved, and the defect pulse is well detected. As the level becomes close to "0" level, it becomes easy to set an appropriate threshold value, and the crest value h of the defect can be measured with good accuracy. Big There is a gift.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a magnetic film defect inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a partial block diagram of FIG.

FIG. 3 is an operation explanatory diagram for FIG. 2;
(a) is an explanatory view of an example of the output signal, and (b) is an explanatory view of the difference signal.

FIG. 4 is a configuration diagram of a surface defect inspection apparatus as a prior art of the present invention.

FIG. 5 is an explanatory diagram of a defect detection method for a magnetic film in a surface defect inspection apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk, 2 ... Rotation mechanism, 3 ... Inspection optical system of surface defect inspection apparatus, 4 ... Signal processing part, 5 ... Data processing part,
51 ... MPU, 52 ... Memory (MEM), 53 ... Printer (P
RT), 6 ... Inspection optical system according to the present invention, 61 ... Projecting system, 62 ... Light receiving system, 611 ... Laser diode (LD), 61
2 ... Beam expander (EX), 613 ... Cylindrical lens (SYL), 614 ... Mirror, 621 ... Objective lens, 622 ... Photodiode array (APD / ARR)
Y), 7 ... Difference calculation unit, L _T ... Laser beam, L _R ... Reflected light of magnetic film, L _R '... Scattered light of defect of magnetic film, L _G ... Ground level, APD ... Avalanche photodiode, DA ... Difference circuit, N ... Noise due to specular reflection light L _R ,
p ... Defect pulse for scattered light L _R ', h ... Crest value of defect pulse, V _S ... Threshold voltage, V _{S +} ... Positive threshold voltage, V _S -... Negative threshold voltage.

Claims (1)

[Claims] 1. A rotating mechanism mounted with a magnetic disk and rotating, and a laser beam band having an appropriate length in the radial direction of the magnetic disk is projected and scanned on a magnetic film of the rotating magnetic disk. A light projecting system, and a light reflected by the magnetic film of the laser light band, which is provided in a direction of a regular reflection angle equal to the incident angle of the light projecting system, and scattered light by a defect existing in the magnetic film. An objective lens for condensing, and a plurality of two provided at the image forming position of the objective lens and corresponding to the laser light band.
n avalanche photodiodes are arranged linearly, and a light receiving system formed of a photodiode array for receiving the collected reflected light and scattered light is provided, and an appropriate two of the 2n avalanche photodiodes are provided. Combining each one, calculating the difference between the output signals of the two avalanche photodiodes of each combination, eliminating the noise due to the reflected light of the magnetic film, and outputting a defect pulse for the scattered light of the defect, A magnetic film defect inspecting apparatus for a magnetic disk, comprising a difference calculation section comprising n difference circuits.