JP2001228094A - Apparatus for inspecting disk surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus for inspecting the surface of a disk, which has reduced background noise and is capable of especially detecting projected fine flaws with high sensitivity. SOLUTION: The apparatus for inspecting the surface of the disk consists of a light surface unit for emitting a laser beam L having a wavelength λ, a proximity optical element 10 having a refractive index (n) arranged at a distance of the wavelength λor shorter from the surface of a disk substrate 1 and a photodetector 16 for detecting the scattered light of the evanescent light from the element 10. The optical axis of laser beam L is set to sin-1 (1/n) or smaller, with respect to a normal line N, and the incident optical axis C2 of the photodetector 16 is set to sin-1 (1/n) or larger with respect to the normal line N.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk surface inspection apparatus, and more particularly, to a disk surface inspection apparatus for inspecting the presence of minute irregularities on a disk surface.

[0002]

2. Description of the Related Art Generally, a hard disk substrate is required to have an extremely smooth surface having an average roughness (Ra) of 0.5 nm. The acceptable defect size is also very small. For example, the size of surface defects caused by scratches and foreign matter adhered during the manufacturing process, deterioration after manufacturing, etc. is as small as 1 μm or less in diameter and 0.1 μm or less in the thickness direction. It is becoming.

In order to manufacture a hard disk substrate of good quality by removing such fine defects, an inspection device with extremely high sensitivity is required.

Conventionally, in order to detect minute defects with high sensitivity, it has been practiced to irradiate the inspection surface with laser light to detect scattered light from the defects. However, in such an inspection method using propagating light, in the case of a disk substrate made of crystallized glass, since scattering occurs inside the substrate, such internal scattering becomes background noise, resulting in high sensitivity. Could not be detected.

[0005] For this reason, there has been proposed a method of irradiating a laser beam to a disk substrate at an angle and narrowing an observation field of view from a direction opposite to an incident direction to perform detection. However, sufficient removal of scattered light (background noise) inside the substrate has not been achieved.

On the other hand, in a hard disk, it is known that a convex defect has a large adverse effect on the characteristics of a hard disk drive, but a concave defect has a relatively small adverse effect and a large allowable defect size. ing. In the conventional scattered light detection method, both a convex defect and a concave defect are detected with the same sensitivity, and the unevenness cannot be distinguished. Therefore, if the sensitivity setting is performed in accordance with the convex defect, the concave defect is determined as a defective product up to the originally allowable defect, resulting in a decrease in yield.

SUMMARY OF THE INVENTION An object of the present invention is to provide a disk surface inspection apparatus which has a small background noise and can detect highly sensitive minute defects in particular.

[0008]

In order to achieve the above object, the disk surface inspection apparatus according to the first invention has a wavelength λ.
Irradiating means for emitting laser light, a proximity optical element disposed at a distance of not more than the wavelength λ from the surface to be inspected of the disk, having a refractive index n, and scattered light of evanescent light leached from the proximity optical element. Light detecting means for detecting the light, the irradiating means irradiating the surface to be inspected via the proximity optical element, and the incident angle of the irradiation light is sin with respect to the normal to the surface of the proximity optical element facing the disk surface. ^-1 (1 / n) or less, and the incident light axis of the light detecting means is set to sin ^-1 (1 / n) or more with respect to the normal line.

In the disk surface inspection apparatus according to the first invention, the surface to be inspected is irradiated with laser light through a proximity optical element made of a material having a high refractive index, and evanescent light scattered on the surface to be inspected is detected by a light detecting means. To detect. This light detecting means detects only scattered light generated at a place near the proximity optical element. Therefore, the surface noise can be detected with high sensitivity and low background noise without being affected by the scattering or the internal defects due to the crystal grains of the disk substrate. Also,
Since the convex defect scatters the evanescent light at a location closer to the proximity optical element than the concave defect, the convex defect can be detected with higher sensitivity.

Further, in the disk surface inspection apparatus according to the first invention, the incident optical axis is sin relative to the normal.
It is preferable to provide another light detecting means set to ^-1 (1 / n) or less. The light detecting means detects the propagated light scattered by the disk, and compares the detected value with the detected value of the evanescent light by the light detecting means to detect a defect with higher accuracy.

Further, in the disk surface inspection apparatus according to the second invention, the radiating means is set so that the incident angle of the illumination light is not less than sin ^-1 (1 / n) with respect to the normal, and the evanescent light is set. The light detecting means for detecting the scattered light is set so that its incident optical axis is not more than sin ^-1 (1 / n) with respect to the normal line.

In the disk surface inspection apparatus according to the second aspect of the present invention, the illumination light from the radiating means is totally reflected inside the proximity optical element made of a high refractive index material, and the evanescent light leaching from the proximity optical element is used. To detect defects on the surface to be inspected. The evanescent light leached from the proximity optical element is scattered by a defect on the surface to be inspected, and the scattered light is detected by the light detecting means. In this case, since the evanescent light leached from the proximity optical element exists only near the proximity optical element, the background noise is small and the sensitivity is high without being affected by scattering or internal defects due to crystal grains of the disk substrate. Surface defects can be detected. In addition, the intensity of the evanescent light that has leached from the proximity optical element due to total reflection is large near the proximity optical element, and decreases as the distance from the proximity optical element increases. Therefore, a convex defect is irradiated with strong light and strongly scattered, and a similar concave defect is scattered weakly, so that a convex defect can be detected with higher sensitivity.

Further, in the disk surface inspection apparatus according to the second invention, the incident optical axis is sin relative to the normal.
It is preferable to provide another light detecting means which is set to ^-1 (1 / n) or more and receives light totally reflected by the proximity optical element. This light detecting means can detect the distance between the surface to be inspected and the proximity optical element because the amount of incident total reflection light changes according to the distance between the proximity optical element and the surface to be inspected. Can be detected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a disk surface inspection apparatus according to the present invention will be described below with reference to the accompanying drawings.

(See First Embodiment, FIGS. 1 and 2) As shown in FIG. 1, the disk surface inspection apparatus according to the first embodiment is close to the surface (non-inspection surface) of the non-inspection disk substrate 1. The first optical detector 15 and the second optical detector 16 are provided so as to irradiate the element 10 with laser light L from a light source unit (not shown).

The non-inspection disk substrate 1 is made of crystallized glass, and is driven to rotate at a constant speed while being clamped on the rotation shaft of the spindle motor 2.

The proximity optical element 10 is made of a glass material having a high refractive index, and has a substantially hemispherical shape with a slight curvature formed on the plane side. In the first embodiment, the refractive index is 1.5
2 BK7 was used as a material. The proximity optical element 10 is controlled so as to move at a constant speed in the radial direction of the disk 1 while maintaining the distance from the surface of the disk substrate 1 to a constant value of 100 nm or less. As such a control method, for example,
A flying slider system generally used conventionally in a hard disk drive can be used.

The light source unit is composed of a laser diode and a collimator lens. Irradiation is performed so as to be incident from the same direction as the line N. In the first embodiment,
Although the laser beam L having a wavelength of 632 nm is used, another wavelength (for example, 488 nm) may be used.

Laser light L incident on the proximity optical element 10
Is condensed near the center of the bottom surface of the element 10, passes through the disk substrate 1, and is partially scattered. If there is a surface defect, the scattering increases. Further, a part of the laser light L oozes from the bottom surface of the element 10 as evanescent light and is scattered on the surface of the disk substrate 1.

[0020] The first optical detector 15, the light receiving element 15a and is constituted by a condenser lens 15b, within an angle θ with respect to the incident optical axis C ₁ is the normal N, specifically normal N At an angle of 15 °. In this specification,
The angle θ means sin ⁻¹ (1 / n), and the element 1
0 represents a divergence angle at which propagation light emitted from a minute area immediately below the center of the bottom surface passes through the element 10 and is scattered. The first photodetector 15 receives both the light scattered by the surface defect of the disk substrate 1 and the light scattered inside the substrate 1 on the light receiving element 15a, and detects the amount of the scattered light.

[0021] The second optical detector 16 is composed of a light receiving element 16a and the condenser lens 16b, the incident optical axis C ₂ is more than the angle θ with respect to the normal N, in particular of 60 ° The angle is set. Light incident from the air outside the proximity optical element 10 does not normally travel in the direction of the second photodetector 16 according to Snell's law. What is detected by the second photodetector 16 is an evanescent light component scattered near the bottom surface of the element 10. That is, in order to take in the evanescent light component scattered by the minute structure on the surface of the substrate 1, the bottom surface of the element 10 is arranged near the surface of the substrate 1, and the scattered evanescent light component is immersed in the element 10. I do. The immersed light propagates freely in the element 10 and can pass through the element 10 and reach the second photodetector 16.

The surface inspection is performed by moving the proximity optical element 10 and the photodetectors 15 and 16 in the radial direction at a constant speed while rotating the disk substrate 1 at a constant speed. At this time, the laser light L condensed in the vicinity of the bottom surface of the element 10 is transmitted and diverged as it is, and irradiates and scatters a defect or the like on the surface or inside of the disk substrate 1. The light scattered by the internal defect or the like is refracted into the element 10 in a direction within the angle θ.
The light does not enter the photodetector 16. The component scattered on the surface of the substrate 1 and turned into evanescent light penetrates into the element 10 to enter the second photodetector 16. Therefore, the surface defect can be identified with high sensitivity without being affected by scattering or the like inside the substrate 1.

Further, the first photodetector 15 detects the amount of the propagation light scattered by the substrate 1 and compares this detected value with the detected value of the second photodetector 16 to obtain higher accuracy. Surface defects can be identified.

FIG. 2 shows a mode of detecting scattered light in the first embodiment. Evanescent light leached from the element 10 is scattered by a convex or concave defect. The light scattered by the minute defect has a strong intensity near the defect, and the intensity rapidly decreases as the distance from the defect increases. As shown in FIG. 2A, since the convex defect has a shape approaching the bottom surface of the element 10, a large amount of scattered light enters the inside of the element 10. As shown in FIG. 2B, since the concave defect has a shape separated from the bottom surface of the element 10, the degree of the scattered light entering the element 10 is small. Therefore, a convex defect having a small allowable width can be detected with high sensitivity.

In the first embodiment, the laser beam L is set to be incident on the element 10 in the vertical direction. However, the laser beam L may be incident on the normal line N within an angle θ.

(See Second Embodiment, FIGS. 3 and 4) As shown in FIG. 3, the disk surface inspection apparatus according to the second embodiment is close to the surface (non-inspection surface) of the non-inspection disk substrate 1. The first optical detector 25 and the second optical detector 26 are provided, and a laser light L is applied to the element 20 from a light source unit (not shown).

As in the first embodiment, the non-inspection disk substrate 1 is made of crystallized glass, and is driven to rotate at a constant speed while being clamped on the rotating shaft of the spindle motor 2.

The proximity optical element 20 is made of a glass material having a high refractive index, and has a substantially hemispherical shape with a slight curvature formed on the plane side. In the second embodiment, the refractive index is 1.5
2 BK7 was used as a material. The proximity optical element 20 is controlled so as to move at a constant speed in the radial direction of the disk 1 while maintaining a constant distance of 100 nm or less from the surface of the disk substrate 1. Such a control method includes the first method described above.
As in the case of the embodiment, a flying slider method generally used conventionally in a hard disk drive can be used.

The light source unit is composed of a laser diode and a collimator lens, and emits a laser beam L of a predetermined wavelength so as to converge near the center of the bottom surface of the element 20. Specifically, the angle of incidence with respect to the normal N is 6
Irradiate so as to be incident at an angle of 0 °. In the second embodiment, the laser beam L having a wavelength of 632 nm is used, but another wavelength (for example, 488 nm) may be used.

Laser light L incident on proximity optical element 20
Are condensed near the center of the bottom surface of the element 20, and are totally reflected and emitted out of the element 20. Further, a part of the laser light L oozes out from the bottom surface of the element 20 as evanescent light,
The light is scattered on the surface of the disk substrate 1. If surface defects exist on the disk substrate 1, scattering increases.

The first optical detector 25, the light receiving element 25a and is constituted by a condenser lens 25b, the following angle θ with respect to its incident optical axis C ₃ the normal N, specifically normal N It is set in the same direction as. The first light detector 25 receives the evanescent light scattered by the surface defect of the disk substrate 1 on the light receiving element 25a, and detects the amount of the scattered light.

The second photodetector 26 is composed of a light receiving element 26a and the condenser lens 26b, so that the incident optical axis C ₄ matches the total reflected light of the optical axis of the element 20 of the laser beam L That is, it is set at a position where the total reflection light is received.

The surface inspection is performed by moving the proximity optical element 20 and the photodetectors 25 and 26 in the radial direction at a constant speed while rotating the disk substrate 1 at a constant speed. At this time, the evanescent light that has permeated near the bottom surface of the element 20 is largely scattered when a convex or concave defect exists on the surface of the disk substrate 1. By detecting the scattered light by the first photodetector 25, a defect on the surface can be identified. The evanescent light that has leached from the proximity optical element 10 exists strongly near the surface of the substrate 1 and only slightly enters the inside of the substrate 1. Accordingly, surface defects can be identified with high sensitivity without being greatly affected by scattering inside the substrate 1.

Further, the amount of the totally reflected light from the proximity optical element 20 is detected by the second photodetector 26. Since the total reflection light quantity changes according to the distance between the surface of the disk substrate 1 and the element 20, this detection value corresponds to the distance between the two. Therefore,
By correcting the detection value of the first photodetector 25 with the detection value of the second photodetector 26, a surface defect can be identified with higher accuracy.

FIG. 4 shows a mode of detecting scattered light in the second embodiment. Evanescent light seeping out of the element 20 is scattered by a convex or concave defect of the element 20. The exuded evanescent light has a strong intensity near the bottom surface of the element 20, and the intensity rapidly decreases as the distance from the bottom surface increases. As shown in FIG. 4A, a convex defect is irradiated with strong light and strongly scattered. On the other hand, FIG.
As shown in (B), the concave defect has a weaker light intensity and is scattered weakly. Therefore, a convex defect having a narrow allowable width can be detected with high sensitivity.

(Other Embodiments) The disk surface inspection apparatus according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention.

In particular, disks to be inspected may be disks made of various materials other than the disk substrate 1 made of crystallized glass shown in the first and second embodiments. The disc may have a recording layer and a protective layer formed thereon. The proximity optical element may have various shapes and configurations other than the shapes shown in the first and second embodiments.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a disk surface inspection apparatus according to a first embodiment.

FIG. 2 is a schematic diagram showing a detection mode of scattered light in the first embodiment.

FIG. 3 is a schematic configuration diagram showing a disk surface inspection device according to a second embodiment.

FIG. 4 is a schematic diagram showing a detection mode of scattered light in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Disc substrate 10, 20 ... Proximity optical element 15, 16, 25, 26 ... Photodetector L ... Laser beam N ... Normal line

Claims (4)

[Claims] 1. A disk surface inspection apparatus for inspecting the presence or absence of minute irregularities on a disk surface, comprising: a radiating means for radiating a laser beam having a wavelength of λ; A proximity optical element having a refractive index n, and light detection means for detecting scattered light of evanescent light leached from the proximity optical element, wherein the radiating means has a surface to be inspected via the proximity optical element. And the incident angle of the irradiation light is set to sin ⁻¹ (1 / n) or less with respect to the normal to the surface of the proximity optical element facing the disk surface. Si to normal
The disk surface inspection apparatus is set to n ⁻¹ (1 / n) or more. 2. The incident optical axis is sin with respect to the normal.
^2. The disk surface inspection apparatus according to claim 1, further comprising another light detection means set to ^-1 (1 / n) or less. 3. A disk surface inspection apparatus for inspecting the presence of minute irregularities on a disk surface, comprising: a radiating means for radiating a laser beam having a wavelength of λ; A proximity optical element having a refractive index n, and light detection means for detecting scattered light of evanescent light leached from the proximity optical element, wherein the radiating means has a surface to be inspected via the proximity optical element. And the incident angle of the irradiation light is set to not less than sin ^-1 (1 / n) with respect to the normal to the surface of the proximity optical element facing the disk surface. Si to normal
A disk surface inspection apparatus, wherein the disk surface inspection apparatus is set to n ^-1 (1 / n) or less. 4. An incident optical axis is sin with respect to the normal.
4. The disk surface inspection apparatus according to claim 3, further comprising another light detection means which is set to ^-1 (1 / n) or more and receives the total reflection light from said proximity optical element.