JP2006138754A - Disc surface inspection method and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for inspecting the determination of existence and uniformity of a texture, which is fine irregularity, processed in both surfaces of a transparent disc substrate made of glass material or the like. <P>SOLUTION: In this method and device, laser beams are radiated to the circumferential texture formed on both surfaces of the disc substrate made of the glass material, and the surface roughness of the disc substrate is measured. The laser beams are collected, the angle between the optical axis of the laser beams coming into the surfaces of the disc substrate and the texture is set square, the scattered light from the disc substrate surface and the scattered light from the disc substrate rear face are received on the sensor, and the scattered light intensity output is calculated based on a light receiving signal and displayed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an inspection apparatus for detecting the surface roughness of a disk substrate, and more particularly to a disk surface inspection method and apparatus for inspecting the surface roughness of a disk substrate that is a recording medium for a hard disk device.

As a magnetic recording medium used in a hard disk device, a disk substrate on which a magnetic material is deposited is used. The disk substrate is magnetized by a magnetic head, and data is recorded and reproduced magnetically. On both sides of this disk substrate, fine irregularities called textures are processed to prevent magnetic head adsorption and improve magnetic properties. This texture is processed before depositing a magnetic material or the like. In the manufacture of hard disk drives, if this disk substrate has no texture or roughness, fatal damage such as damage to the disk substrate due to magnetic head adsorption or signal failure due to head flying failure Defects will occur. It is important to eliminate defective products immediately after texturing because defects occur in a state where a magnetic material or the like is deposited, which is disadvantageous in terms of cost.

As a conventional texture measurement method, surface roughness measurement using an AFM (Atomic Force Microscope) is generally used. In the AFM measurement, the throughput is remarkably slow and the entire disk substrate cannot be easily inspected. In addition, there are problems that the measurement probe is a consumable item and the measurement reproducibility varies due to the probe consumption.

Therefore, in the mass production process, there is a demand for a disk surface inspection apparatus that has a high throughput and is capable of 100% inspection and can measure fine irregularities in order to stably manufacture the disk substrate.
As a method for measuring the surface roughness of a disk substrate, currently, as shown in Patent Document 1 (Japanese Patent Publication No. 2003-528413), the surface of the disk substrate on which a thin film is deposited is irradiated with light, and the scattered light is Some of them collect light with a scatterometer and detect the thickness, deterioration, wear, etc. of the thin film formed on the surface from the obtained signal intensity distribution. According to this method, it is possible to detect a deep or abnormal texture on the disk substrate. This is possible by detecting a change in the refractive index by changing the ratio of the polarization of the illumination light because the deep or abnormal texture has less carbon or has contaminants.

However, with this method, it is possible to detect the presence or absence of abnormalities, but since the detection of uniformly processed texture does not cause a change in refractive index, the texture is not processed completely on the entire surface. There is a problem that it cannot be identified whether it is processed.

In addition, non-patent literature 1 (Jpn. J. Appl. Phys. Vol. 32 (1993) pp.
.352-357), an apparatus using a CCD camera is disclosed. This device is L
It is possible to detect minute foreign matter of about several tens of nanometers adhering to the SI wafer. But LS
Since I is generally arranged in the X and Y directions, if this is used to inspect the texture of the disk substrate, the optical axis of the incident laser beam and the surface of the disk substrate are moved when the measurement position is moved. Since the angle formed by the texture streaks formed in the circumferential direction of the substrate fluctuates in a certain direction in the horizontal plane and the vertical plane of the substrate, the intensity of the scattered light also varies. Naturally, since the measurement algorithm is for determining the presence or absence of foreign matter, the surface roughness of the texture cannot be measured.

As described above, the disk substrate or wafer surface inspection technology using the conventional inspection method cannot determine the presence or absence of the texture or the surface roughness of the disk substrate that has been processed uniformly. The generation of defective products is inevitable, and the manufacturing yield of the disk substrate is lowered.

Special Table 2003-528413 Publication Fine Particle Inspection Down to 38nm Bare Wafer with Micro Roughness by Side-Sccttering Light Detection (Jpn. J. Appl. Phys. Vol. 32) 1993) pp. 352-357)

The surface roughness of the disk substrate tends to become smaller due to the improvement of the surface recording density and the miniaturization of the hard disk device. Also, the material of the disk substrate is shifting from a conventional aluminum alloy to a glass material having high rigidity. Therefore, there is a need for a non-destructive, high-accuracy, high-speed, and reproducible measurement method for a transparent disk substrate such as a glass material.

Furthermore, in the foreign matter inspection device for semiconductor wafers, the lateral resolution of measurement is high, but LSIs are generally arranged in the XY direction, so if this is used to inspect the texture of a disk substrate, the measurement position The angle between the optical axis of the incident laser beam and the texture streaks formed in the circumferential direction of the disk substrate surface fluctuates in a certain direction in the horizontal and vertical planes of the substrate. Since the intensity of scattered light also fluctuates, it cannot be measured with high accuracy.

Therefore, the problem to be solved by the present invention is to provide an apparatus for inspecting the presence / absence of a texture, which is a minute unevenness processed on both sides, on a transparent disk substrate such as a glass material, and determination of uniformity. is there. The present invention also provides a method of manufacturing a disk substrate capable of sorting out defects in the texture of the disk substrate and reducing the occurrence of defective disk substrates by the above-described inspection method and inspection apparatus. It is to be.

In order to solve the above problems, in the present invention, a method of measuring the surface roughness of a disk substrate by irradiating laser light to the circumferential texture formed on both sides of the disk substrate made of glass. In the apparatus, the laser beam is focused, the optical axis of the laser beam incident on the surface of the disk substrate and the texture angle are perpendicular, and the scattered light from the disk substrate surface and the scattered light from the back surface of the disk substrate are placed on the sensor. The scattered light intensity output was calculated from the received light signal, and the scattered light intensity output was displayed.

In addition, a sensor capable of photoelectric conversion is used as the sensor. Further, the incident angle of the laser light incident on the surface of the disk substrate was set to 20 degrees to 30 degrees. In the method of manufacturing a magnetic disk substrate, the disk substrate whose texture is not processed and whose distribution is determined to be non-uniform by the above-described method and apparatus is discharged from the manufacturing process.

According to the present invention, it is possible to determine whether double-sided inspection is possible by simultaneously detecting both sides of the scattered light from the texture processed on the disk substrate of the glass material, and it is possible to further reduce the measurement time, There is an effect that it is possible to inspect the surface roughness of the disk substrate with high reliability. In addition, since it is possible to easily determine a processing defect on only one side, there is an effect of discharging a defective product in a single inspection.

  The best mode for carrying out the present invention will be described below.

An embodiment of a disk surface inspection method and apparatus according to the present invention is shown in FIG. The present apparatus and method are directed to a disk substrate made of a glass material before forming a magnetic material or the like. The disk substrate 1 is fixed to the rotary stage 2 by a method not shown. The mechanism part to be fixed has a structure that does not appear on the surface of the disk substrate 1. The rotary stage 2 is fixed to a horizontal stage 3 that can move in the horizontal direction with respect to the paper surface. The laser light source 4 includes, for example, a YAG double wave laser having a wavelength of 532 nm, a visible light laser of a laser diode having a wavelength of 400 to 410 nm, or a wavelength of 350 nm.
An ultraviolet laser having a wavelength of about 266 nm or a far ultraviolet laser having a wavelength of about 266 nm is used. The laser light passes through the laser shutter 5 that can block the light beam, passes through the beam expander 6 that can expand the laser light to a certain size, and can adjust the amount of light emitted by the light amount adjustment filter 7.
The expanded laser light is narrowed down by the condenser lens 8 and irradiated onto the surface of the disk substrate 1 by a light beam 10 from an oblique direction by an oblique mirror 9. The focused light beam is determined by the wavelength of the laser beam, the beam diameter, and the focal length of the condenser lens. In this example, it was set to about 100 microns. The objective lens 11 is installed above the position to be illuminated. Objective lens 11
Then, the surface of the disk substrate 1 is imaged on the sensor unit 13 by the imaging lens 12. The computer 14 can control the rotary stage 2, the horizontal stage 3, the laser shutter 5, the light amount adjustment filter 7, and the sensor unit 13, and has a processing device that can accumulate and analyze the output results of the sensor unit 13. Further, position information of the rotary stage 2 and the horizontal stage 3 can be stored.
Various inspection parameters can be input by the input means 15. The display means 16 can display a detection result display, an input screen, and the like.

FIG. 2 shows the relationship between the disk substrate 1 and the illumination light beam 10. On the disk substrate 1, a texture 50, which is a minute uneven portion, is processed on the entire surface on the circumference. The texture is uneven with a pitch of 50 nm or less and an arithmetic average surface roughness (Ra) of 1 nm or less. The illumination light beam 10 forms a spot 17 on the disk substrate 1 by the condenser lens 8 and the oblique mirror 9 shown in FIG. The illumination light beam 10 and the texture 50 are set to be perpendicular to each other.

FIG. 3 shows the detection concept. The light beam 10 illuminates the texture 50 of the disk substrate 1 from an oblique direction. When the disk substrate 1 is made of a transparent glass material, the illumination light beam 10 transmits part of light as transmitted light 18 on the opposite side and part of light reflects as reflected light 19. The unevenness of the texture 50 is diffracted by the uneven portion on the surface by being arranged at right angles to the illumination light beam 10, and the scattered light 20 is generated. Light generated above the scattered light 20 is captured by the objective lens 11. Objective lens 11
The light captured in step 1 is condensed on the sensor unit 13 by the imaging lens 12 and photoelectrically converted by the sensor unit 13 so that the surface information of the disk substrate 1 can be detected.

FIG. 4 shows the scattering intensity due to the change in the angle of the illumination light beam 10 obtained by simulation. The horizontal axis is the incident angle. The incident angle is 0 degree when incident on the disk substrate 1 in the horizontal direction and 90 degrees on the objective lens side. The vertical axis represents the scattering intensity and is a relative value. In the figure, it can be seen that the scattering intensity is highest at an incident angle of 20 to 30 degrees and there is no significant change. Therefore, scattered light can be efficiently generated if illumination is performed at an angle close to this. In this example, the incident angle was set to 20 to 30 degrees.

5a and 5b show examples of images detected by the sensor 13 according to this embodiment. Each is an example of an image when a CCD camera is used as the sensor 13. FIG. 5a shows the result of detecting a disk substrate that has not been textured. The detected image and the waveform of the cross section AA are shown, the horizontal axis represents pixels, and the vertical axis represents luminance. Since no diffracted light is generated, the overall brightness is low. FIG. 5b shows the result of detecting a disk substrate with a texture processed. Similarly, the detected image and the waveform of the cross section AA are shown. In the detected image, the vertical lines of the texture 50 regularly arranged are detected,
A change in brightness is detected. Thus, it can be seen that the detected light amount changes depending on the presence or absence of the texture.

FIG. 6 shows an example in which a photoelectric conversion sensor is used as the sensor 13 according to this embodiment. The disk substrate 1 is stationary. The horizontal axis represents the sampling time, and the vertical axis represents the sensor output. Waveform 21
FIG. 5A shows a waveform when a state in which the texture is not processed on the disk substrate 1 shown in FIG. 5A is detected. A waveform 22 is a state in which the texture shown in FIG.

FIG. 7 shows the sensor output when the surface roughness of the texture is different. The horizontal axis represents the surface roughness (Ra) of the texture, and the vertical axis represents the sensor output. Similar to FIG. 6, in the waveform 24, when the texture is not processed, the sensor output becomes near 0, and the sensor output increases as the surface roughness (Ra) increases, and the surface roughness (Ra) and the sensor output increase. It can be seen that there is a correlation. For example, when the surface roughness (Ra) changes in the example of FIG. 7, if the threshold value 25 is set, a surface roughness (Ra) of 0.3 nm or less below the threshold value 25 can be excluded as a defective product. Become.

FIG. 8 shows the change of the optical axis in the disk substrate made of glass. The texture 50 is processed on the front surface of the disk substrate 1 and the texture 51 is processed on the back surface. When the illumination light beam 10 is irradiated on the disk substrate 1 from an oblique direction, it is separated into a light beam 19 reflected on the surface and a light beam 26 incident on the inside of the glass. The light beam 26 is separated into a light beam 18 that exits on the back surface and a light beam 27 that reflects on the back surface. The light beam 27 is separated into a light beam 28 that exits on the surface and light that is reflected internally again. The light beam advances while repeating this reflection. In the surface texture 50, scattered light 20 is generated by the first light beam 10. Scattered light 29 is generated inside the disk substrate 1 by the light flux 26 with the texture 51 on the back surface. Furthermore, the scattered light 30 is generated again by the light flux 27 in the surface texture 50. When the disk substrate 1 is observed from the upper surface, the first scattered light 20 becomes a spot 31 and the scattered light 29 on the back surface is observed like a spot 32 because the glass is transparent. Further, the scattered light 30 generated again on the surface becomes a spot 33. The spot interval P is calculated by wavelength, incident angle, thickness, and material. The spot 32 from the back surface is ½ of the pitch P. Since the scattered light 30 is scattered by a light beam that has been repeatedly reflected and refracted, the amount of light is considerably reduced.

FIG. 9 shows the detection range of the objective lens 11. The detection field 34 of the objective lens 11 is set so that spots 31 and 32 can be detected simultaneously on the disk substrate 1.

  An embodiment of the sensor unit 13 in FIG. 1 will be described with reference to FIGS.

FIG. 10 shows an embodiment of the sensor unit 13. Since the generation state of the scattered light on the disk substrate 1 is the same as that in FIG. 8, the description is omitted. The mirror 100 is provided with a pinhole 101 through which the spot 31 can be transmitted. The light transmitted through the pinhole 101 enters the photomultiplier tube 102. The photomultiplier tube 102 is driven by a high-voltage power source 103, and the current-voltage conversion circuit 104 converts the current obtained by the photoelectron multiplier tube 102 into a voltage and outputs it. Further, the light flux of the spot 32 is reflected by the mirror 100. Similarly, the photomultiplier tube 105 is a high voltage power source 10.
6, and the current / voltage conversion circuit 107 converts the current obtained by the photoelectron multiplier 105 into a voltage and outputs the voltage. Therefore, the photomultiplier tube 102 can detect the spot 31 and the photomultiplier tube 105 can detect the spot 32. Since the spot 32 described with reference to FIG. 8 is out of the detection visual field described with reference to FIG. 9, the light beam does not reach the sensor unit 13.

The operation in this configuration will be described. FIG. 11 shows an example of the outputs of the current / voltage conversion circuits 104 and 107. The waveform without texture is 200. For example, the case where the texture is processed on both sides will be described. The output of the current-voltage conversion circuit 104 is a waveform 201. Since the texture 50 is processed on the surface, scattered light is generated on the surface, and the sensor output increases. The output of the current-voltage conversion circuit 105 is a waveform 202. Since the texture 51 is also processed on the back surface, scattered light is generated on the back surface, and the sensor output increases similarly. For example, when the texture is processed only on the surface, the output of the current-voltage conversion circuit 104 is a waveform 201.
However, the output of the current-voltage conversion circuit 107 has a waveform 200 because scattered light is not generated. Similarly, when the texture is processed only on the back surface, the output of the current-voltage conversion circuit 104 has a waveform 200. As a result, it is possible to determine whether texture processing is performed on the front surface, back surface, or both surfaces.

FIG. 13 shows another embodiment of the sensor unit 13. The generation state of scattered light on the disk substrate 1 is
Since it is the same as FIG. 8, description is omitted. The light shielding plate 108 is provided with a pinhole 109 through which the spot 31 can be transmitted and a pinhole 110 through which the spot 32 can be transmitted. Shutter 111
Can move to the top of the pinhole 110 by a method not shown, and block the light flux of the spot 32. The light flux that has passed through the pinholes 109 and 110 enters the photomultiplier tube 102. The photomultiplier tube 102 is driven by a high-voltage power source 103, and the current-voltage conversion circuit 104 converts the electrons obtained by the photoelectron multiplier tube 102 into a voltage and outputs the voltage.

The operation in this configuration will be described. FIG. 14 shows an example of the output of the current / voltage conversion circuit 104. First, a waveform is acquired with the pinhole 110 open. Next, the shutter 111 is driven, and a waveform in a state where the pinhole 110 is blocked is acquired. Under this condition, the sensor output waveform in the state without texture is 203. When the pinhole 110 is open and the texture is processed on both sides, the sensor output is a waveform 204. Pinhole 1
When 10 is cut off, the sensor output becomes a waveform 205, and when the pinhole 110 is cut off, the sensor output decreases. For example, when the texture is processed only on the surface, the waveform 205 of the sensor output is obtained when the pinhole 110 is open. Even when the pinhole 110 is cut off, the sensor output becomes the waveform 205. Similarly, when the texture is processed only on the back surface, the sensor output when the pinhole 110 is open is a waveform 205, and the sensor output when the pinhole 110 is blocked is a waveform 203. As a result, it is possible to determine whether texture processing is performed on the front surface, back surface, or both surfaces.

FIG. 14 shows another embodiment of the sensor unit 13. The generation state of scattered light on the disk substrate 1 is
Since it is the same as FIG. 8, description is omitted. The line sensor 112 is installed so that the spot 31 and the spot 32 can be detected simultaneously. The output of the line sensor 112 is photoelectrically converted by the A / D converter 113.

The operation in this configuration will be described. FIG. 15 shows an example of the output of the A / D converter 113 without texture. The horizontal axis represents pixels, and the vertical axis represents sensor output. Since the scattered light is not detected, the sensor output is constant and the waveform 206 is obtained. Next, FIG. 16 shows an example of the output of the A / D converter 113 at the time of texture detection. Sensor output when texture is processed on both sides is waveform 2
The peak 208 is detected in the texture 50 on the front surface, and the peak 209 is detected in the texture 51 on the back surface. For example, when the texture is processed only on the front surface, the peak 209 is not detected, and when the texture is processed only on the back surface, the peak 208 is not detected. If the pixel is divided into two ranges and peaks are detected in the ranges 210 and 211, it is possible to determine whether texture processing has been performed on the front surface, the back surface, or both surfaces.

FIG. 17 shows an embodiment of the inspection method in this embodiment. In order to perform high-speed inspection, a spiral system is used in which the disk substrate 1 is rotated while being horizontally moved so as to move by the distance of the spot 17 after one rotation, and the spiral 211 is inspected.

  The operation of the above configuration will be described.

FIG. 18 shows a flowchart of inspection in this embodiment. A disk substrate 1 to be inspected is set on a rotary stage 2. The horizontal stage 3 is moved to the inspection start position, and the disk substrate 1
Rotate. The laser shutter 5 is opened and the disk substrate 1 is irradiated with laser light. The output of the sensor unit 13 is determined to determine whether the texture is processed on both sides. When both sides are not processed, when only one side is processed, it is excluded as a defective product. If both sides are processed, the entire stage is inspected while the horizontal stage 3 and the rotary stage 2 are synchronized.
After completion of the inspection, the laser shutter 5 is closed and the disk substrate 1 is removed.

FIG. 19 shows an example of the inspection result. The horizontal axis represents the inspection position, and the vertical axis represents the sensor output. On the surface of the disk substrate 1, a change in the amount of light such as a waveform 212 is detected. In order to determine this result, the threshold 213 is set to the waveform 212. It is determined whether the waveform 212 is above or below the threshold value 213. In the lower case, it is determined that the desired texture has not been processed, and is regarded as a defective product. In the above case, it is determined as a non-defective product, and the change in the luminance direction at each position of the waveform 212 is obtained. These are processed at high speed by the computer 14.

FIG. 20 shows an example of the display unit 16. The entire disk map, inspection conditions, inspection results, etc. are displayed. The entire disk map is obtained by mapping changes in the luminance direction at each position of the waveform 212 obtained in FIG.

It is a front view which shows schematic structure of the disk surface inspection apparatus of this invention. It is the figure which showed the direction of the illumination and the texture in the Example of this invention. It is a conceptual diagram of the detection in the Example of this invention. It is the figure which showed the relationship between the incident angle and scattering intensity in the Example of this invention. It is the figure which showed an example of the detection image by CCD in the Example of this invention, and showed the cross section AA. FIG. 5 is a diagram showing an example of a detection image by CCD in the embodiment of the present invention and showing a cross section BB It is the figure which showed an example of the detection by the photoelectric conversion sensor in the Example of this invention. It is the figure which showed the relationship of the AFM average surface roughness and sensor output by the Example of this invention. It is a figure explaining the optical path of the illumination light by the Example of this invention. It is a figure which shows the visual field of the objective lens in the Example of this invention. It is one Example of the sensor part in this invention. It is a figure which shows the example of an output of the sensor detected in FIG. It is one Example of the sensor part in this invention. It is a figure which shows the example of an output of the sensor detected in FIG. It is one Example of the sensor part in this invention. It is a figure which shows the example of an output of the sensor detected in FIG. It is a figure which shows the example of an output of the sensor detected in FIG. It is the figure which showed the example of the test | inspection method in this invention. It is the figure which showed the flowchart of the test | inspection in this invention. It is the figure which showed the waveform of the test result in this invention. It is the figure which showed an example of the display in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Disc substrate, 2 ... Rotary stage, 3 ... Horizontal stage, 4 ... Laser light source, 5 ... Laser shutter, 6 ... Beam expander, 7 ... Light quantity adjustment filter, 8 ... Imaging lens, 9 ... Oblique mirror, 11 ... objective lens, 12 ... imaging lens, 13 ... sensor unit, 14 ... computer, 50, 51 ... texture, 102, 105 ... photomultiplier tube.

Claims (6)

In the method of measuring the roughness of the texture formed in the circumferential direction on both surfaces of the glass disk substrate by irradiating the surface of the transparent glass disk substrate with laser light,
Means for focusing the laser beam on a glass disk substrate; means for irradiating the focused laser beam at right angles to the texture; means for detecting surface scattered light of the irradiated laser beam; and laser light transmitted through the glass disk substrate. Means for detecting the scattered light generated on the back surface, means for condensing the scattered light on both sides in the previous period on the photoelectric converter, means for accumulating the output from the photoelectric converter, and storing the data of the accumulated means on the surface. A disk surface inspection method, comprising: means for converting the height into a diameter; and means for determining whether the product is non-defective or defective based on the result of the converted means. 2. The disk surface inspection method according to claim 1, wherein the laser light source is visible light, ultraviolet light, or far ultraviolet light. 2. The disk surface inspection method according to claim 1, wherein the means for condensing the scattered light on both sides onto the photoelectric converter can be simultaneously detected. In the apparatus for measuring the roughness of the texture formed in the circumferential direction on the front and back surfaces of the glass disk substrate by irradiating the surface of the transparent glass disk substrate with laser light,
Means for focusing the laser beam on a glass disk substrate; means for irradiating the focused laser beam at right angles to the texture; means for detecting surface scattered light of the irradiated laser beam; and laser light transmitted through the glass disk substrate. Means for detecting the back scattered light, means for condensing scattered light from the front and back surfaces of the previous period on the photoelectric converter, means for accumulating the output from the photoelectric converter, and the data of the accumulated means for surface roughness A disk surface inspection apparatus comprising: means for converting to: and means for determining a non-defective product or a defective product based on the result of the converted means. 2. The disk surface inspection apparatus according to claim 1, wherein the laser light source is visible light, ultraviolet light, or far ultraviolet light. 2. The disk surface inspection apparatus according to claim 1, wherein the means for condensing the scattered light on both sides onto the photoelectric converter can be detected simultaneously.

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