JP2009211751A - Surface evaluation method of optical disk and surface evaluating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface evaluation method of an optical disk, which is not influenced by light reflected from a rear face of a substrate, and to provide a surface evaluating device which materializes the surface evaluation method. <P>SOLUTION: An interferometer 100 is set up in such a way that an optical axis of measure light is tilted at a tilt angle of Φ<SB>0</SB>toward a surface of an optical disk substrate 150 which is an object to be measured. Whereas, diffracted light DF is emitted at an angle of Φ<SB>1</SB>with respect to the virtual normal VL extending from the surface of the substrate 150. When the tilt angle of the interferometer 100 is set so as to satisfy equation Φ<SB>0</SB>=Φ<SB>1</SB>, the diffracted light DF is made incident on the interferometer 100. Projections and depressions of the surface is evaluated by observing interference fringes produced by the interference of diffracted light DF and reference light RF. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for optically detecting and evaluating defects on the surface of an optical disk, and an evaluation apparatus for optically detecting defects on the surface of an optical disk by the method.

  An optical disc such as a recordable CD (CD-R), a recordable DVD (DVD ± R) or a write-once Blu-ray disc (BD-R) has a recording layer, a reflective layer, and a necessary layer on one surface of a disc-shaped substrate. Accordingly, a protective layer is formed. In addition, a spiral or concentric guide groove called a groove is formed on one surface of the substrate, and a convex part called a land is formed between adjacent grooves. In such an optical disc, recording is performed by irradiating a recording laser beam on the recording layer on the groove to form pits. The length of the pits and the length of the portion (space) between the pits These arrays are reproduced by irradiating a reproduction laser beam, photoelectrically converting the reflected light and reading it as a reproduction signal.

In such an optical disc, the interval between grooves formed on the substrate, that is, the track pitch becomes narrower as the recording capacity increases. For example, a DVD-R having a recording capacity of 4.7 GB on one side has a track pitch of 0.74 μm, whereas a BD-R having a recording capacity of 25 GB on one side has a track pitch of 0.32 μm. is there. Further, such an optical disc has a high demand for high-speed recording, and has been demanded to cope with, for example, 16 times speed. For this reason, in manufacturing the substrate, high accuracy is required when the groove is formed.

In such an optical disc, unevenness may be formed on the surface on which the groove of the substrate is formed due to variations in production. Hereinafter, unless otherwise specified, the surface of the substrate on which the groove is formed is referred to as the surface. When an optical disk using a substrate having an uneven surface is irradiated with a recording laser beam and a reproducing laser beam, a deviation from the target position occurs in the focal position of the laser beam due to thickness variation due to the unevenness. This deviation causes a focus error such as spherical aberration and defocus, and a tracking error. The focus error and the tracking error have an influence such that data writing to the optical disk and data reading from the optical disk are not normally performed, such as a data decoding error. In particular, in recent years, as described above, the recording / reproducing speed of the optical disk has been increased, and the influence has been further increased. Therefore, in order to prevent these errors, it is necessary to evaluate the surface of the substrate of the optical disk.

As a method for evaluating the unevenness of the surface of the substrate of such an optical disc, as disclosed in Japanese Patent Application Laid-Open No. 2005-114630, the surface of the substrate is irradiated with laser light, and the reflected light or diffracted light is emitted. There has been proposed a method for detecting defects by detecting them. For detecting such a defect, an interferometer such as a Michelson interferometer or a Fizeau interferometer is used.

JP 2005-114630 A

However, when the surface of a light-transmitting substrate is evaluated by these methods, there are the following problems. When measuring light is irradiated onto a light-transmitting substrate, the reflected light reflected by the substrate surface and reflected by the back surface of the substrate is detected along with the reflected light reflected by the substrate surface and the diffracted light from the groove on the substrate surface. Is done. In the conventional method, as shown in FIG. 6, the reflected light REF1 or diffracted light on the front surface and the reflected light REF2 from the back surface are superimposed and detected.

The reflected light REF2 from the back surface reflects the unevenness of the back surface and is at substantially the same level as the reflected light REF1 on the front surface. For this reason, if the reflected light REF1 on the front surface and the reflected light REF2 on the back surface cause multiple interference, it becomes impossible to accurately measure the surface irregularities.

Therefore, the present invention proposes a method for evaluating the surface of an optical disk that is not affected by the reflected light from the back surface, and also proposes a surface evaluation apparatus that can realize such an evaluation method.

  In the present invention, as a first solving means, in a method for evaluating the surface of an optical disc having a substrate having a spiral guide groove formed on one surface, a light source that generates measurement light, and a measurement emitted from the light source A beam splitter that reflects a diffracted light returned from the substrate while reflecting a part of the light and transmitting the other, and interferes with the diffracted light returned from the substrate and a part of the measurement light. An interferometer having an imaging device that captures the interference fringes formed and a reflector that reflects a part of the measurement light reflected by the beam splitter or the diffracted light toward the imaging device. The measurement light is irradiated with the optical axis of the interferometer tilted with respect to the surface of the substrate, the tilt of the optical axis of the interferometer at this time, and the tilt angle of the optical path of the diffracted light, Are the same Suggest surface evaluation method of the optical disk was made to be.

The interferometer disclosed in the first solution has a structure in which a part of the measurement light emitted from the light source is used as reference light and is measured by causing interference with the light returned from the object to be measured. . When such an interferometer is tilted with respect to the substrate to be measured, the reflected light from the substrate does not return to the interferometer. However, the diffracted light returns in a direction different from the reflected light, for example, in a direction where the interferometer is located. At this time, if the tilt of the optical axis of the interferometer and the tilt angle of the optical path of the diffracted light are made the same, the optical path of the diffracted light coincides with the optical path of the measurement light, and the reference light and the diffracted light interfere with each other to capture the image Taken at. The surface irregularities can be evaluated by the interference fringes thus photographed. According to the first solving means, the unevenness on the surface of the substrate can be evaluated without being affected by the reflected light from the back surface of the substrate.

Further, in the present invention, as a second solution, in addition to the first solution, the tilt angle of the optical axis of the interferometer with respect to the virtual perpendicular of the substrate is Φ ₀ , and the diffraction with respect to the virtual perpendicular of the substrate Φ ₀ = Φ ₁ = sin ⁻¹ (nλ / 2P) (n is the diffracted light) where Φ _{1 is} the inclination angle of the optical path of the light, P is the distance between the guide grooves of the substrate, and λ is the wavelength of the measurement light. A method for evaluating the surface of an optical disc is proposed. According to the second solving means, when Φ ₀ = Φ ₁ = sin ⁻¹ (nλ / 2P) is satisfied, the diffracted light returned from the surface of the substrate is transferred to the interferometer along the optical path of the measurement light. It becomes incident.

Further, in the present invention, as a third solution, in a surface evaluation apparatus for an optical disc having a substrate having a spiral guide groove formed on one surface, a light source that generates measurement light and measurement light emitted from the light source A beam splitter that reflects a part of the light beam and reflects the diffracted light returned from the substrate, and causes the diffracted light returned from the substrate to interfere with a part of the measurement light. An interferometer having an imaging device that captures the interference fringes formed and a reflector that reflects part of the measurement light reflected by the beam splitter or the diffracted light toward the imaging device, The interferometer is installed such that its optical axis is inclined with respect to the surface of the substrate, and the angle of inclination of the optical axis of the interferometer with respect to a virtual perpendicular extending from the surface of the substrate is Φ ₀ , Φ ₀ = Φ ₁ = sin ⁻¹ (nλ /) where Φ _{1 is} the tilt angle of the optical path of the diffracted light with respect to a virtual perpendicular extending from the surface, P is the distance between the guide grooves of the substrate, and λ is the wavelength of the measurement light. 2P) (n is the order of the diffracted light), an optical disk surface evaluation apparatus is proposed.

According to the third solving means, the unevenness on the surface of the substrate can be evaluated without being affected by the reflected light from the back surface of the substrate using the first and second solving means.

  ADVANTAGE OF THE INVENTION According to this invention, the surface evaluation method of the optical disk which can evaluate the unevenness | corrugation of a surface, without being influenced by the reflected light from a back surface is realizable. Moreover, the surface evaluation apparatus which can implement | achieve such an evaluation method can be obtained.

An embodiment according to a surface evaluation method and an evaluation apparatus for an optical disc of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic diagram of an optical disk evaluation apparatus according to the present invention.

  The evaluation apparatus of the present invention includes a light source 101 that generates measurement light, a beam splitter 102 that divides a part of incident light by reflecting and transmitting others, and light returned from the object to be measured and reference light. Is provided with an interferometer 100 having an imaging device 103 that captures interference fringes formed by interference with each other and a reflecting plate 104 that reflects light reflected by the beam splitter 102 toward the imaging device 103. The light source 101 is connected to control means (not shown). The imaging device 103 is connected to a display device (not shown) such as a monitor, and displays the observed interference fringes. As the light source 101, laser light or the like can be used. As the imaging device 103, a camera using a CCD, a CMOS sensor, or the like can be used. In FIG. 1, lenses such as a collimator lens and a condenser lens are omitted for convenience.

In the evaluation apparatus of the present invention, the interferometer 100 is installed such that the optical axis of the measurement light is inclined with respect to the surface of the optical disk substrate 150 that is the object to be measured. The inclination angle is set to Φ ₀ with respect to a virtual perpendicular VL extending from the surface of the substrate 150. By tilting the interferometer 100 in this way, the reflected light from the back surface of the substrate 150 does not return to the interferometer. On the other hand, the surface of the substrate 150 is the same as the diffraction grating because guide grooves are formed at a predetermined track pitch. Therefore, diffracted light is generated. The optical path of the generated diffracted light has an inclination angle of Φ ₁ with respect to the virtual perpendicular VL. The optical path of the diffracted light is partly in the same direction as the reflected light, but the other part is in the direction in which the interferometer 100 is present. Here, when the tilt angle of the interferometer is set so that Φ ₀ = Φ ₁ , the diffracted light enters the interferometer 100. Since the substrate 150 is similar to the diffraction grating in the radial direction, the measurement light from the interferometer 100 is irradiated from the radial direction of the substrate 150.

  Next, the operation of such an evaluation apparatus will be described. First, the measurement light MB1 is emitted from the light source 101. A part of the light MB2 is reflected by the beam splitter 102 and the rest of the measurement light MB1 is transmitted and irradiated onto the substrate 150. A part of the light MB2 is reflected by the reflecting plate 104 and is incident on the imaging device 103 as reference light RF.

On the other hand the measurement light MB1 is irradiated at an inclination angle [Phi ₀ to the substrate 150. Subsequently, the diffracted light DF is generated by the guide groove on the surface of the substrate 150 and is emitted at an inclination angle Φ ₀ . Here, since Φ ₀ = Φ _{1, the} diffracted light DF enters the interferometer 100. The diffracted light DF incident on the interferometer 100 is reflected by the beam splitter 102 and incident on the imaging device 103. At this time, the diffracted light DF and the reference light RF cause interference. An image generated by the interference between the diffracted light DF and the reference light RF is taken by the imaging device 103.

  Subsequently, the surface of the substrate 150 is scanned by rotating the substrate 150 rotatably installed by a rotation mechanism 151 and a fixing means such as a turntable (not shown). Thereby, interference fringes as shown in FIG. 2 or FIG. 3 are observed. Note that the rotation mechanism 151 is not particularly required to be interlocked with or integrated with the evaluation apparatus, but may be interlocked with or integrated with the evaluation apparatus. As the rotating mechanism 151, a spindle motor or the like is used.

  The interference fringes observed in this way are schematically shown in FIG. 2 or FIG. FIG. 2 shows a state in which the surface of the substrate 150 has no irregularities. When there is no uneven defect on the surface of the substrate 150, interference fringes are observed in which stripes having substantially the same width are arranged concentrically at substantially equal intervals.

  FIG. 3 shows a state where the surface of the substrate 150 has irregularities. When the surface of the substrate 150 has a concavo-convex defect, portions A, B, C, and D in which the shape of the stripe is distorted, such as the interval between the stripes or the width of the stripe, are generated. The size of the distorted portion of such interference fringes varies depending on the height and area of the concavo-convex defect. The evaluation of the substrate 150 can be performed based on the number and size of the distorted portions of the interference fringes. That is, the surface of the substrate 150 can be evaluated by visually observing the state of interference fringes.

Here, a method for matching the tilt angle Φ ₀ of the interferometer with the tilt angle Φ ₁ of the optical path of the diffracted light will be described with reference to FIG. When the measurement light MB having the wavelength λ is irradiated at the incident angle Φ ₀ onto the substrate 150 having the guide grooves GV formed on the surface with the track pitch P, the diffracted light DF is emitted at the output angle Φ ₁ . The relationship at this time is as follows: Φ ₀ and Φ ₁ are angles with respect to a virtual perpendicular VL extending from the surface of the substrate 150.
P × sinΦ ₀ + P × sinΦ ₁ = nλ (1)
It can be expressed by the following formula. Note that n in nλ indicates the order of the diffracted light, and n = 1 if it is the first-order diffracted light.

Here, assuming that Φ ₀ = Φ ₁ , the equation (1) is expressed as follows: sin Φ ₀ = nλ / 2P (2)
It becomes. From the equation (2), Φ ₀ = Φ ₁ = sin ⁻¹ (nλ / 2P) is obtained. That is, if the condition satisfies this equation, the tilt angle Φ _{0 of the} interferometer and the tilt angle Φ ₁ of the optical path of the diffracted light can be matched. For example, when the surface of a BD-R substrate with a track pitch of 0.32 μm is measured with a first-order diffracted light with a laser beam having a wavelength of 405 nm, n = 1, λ = 405 (nm), and P = 320 (nm). Φ ₀ = Φ ₁ ≈39.25 °.

  Next, another example of the embodiment according to the evaluation apparatus of the present invention will be described with reference to FIG. The difference from the previous embodiment is that the direction of the beam splitter 102 is reversed. The operation of another example evaluation apparatus is as follows.

  First, the measurement light MB1 is emitted from the light source 101. A part of the measurement light MB1 is transmitted through the beam splitter 102 and irradiated onto the substrate 150. The remaining part is reflected by the beam splitter 102 and enters the imaging device 103 as reference light RF.

On the other hand the measurement light MB1 is irradiated at an inclination angle [Phi ₀ to the substrate 150. Subsequently, the diffracted light DF is generated by the guide groove on the surface of the substrate 150 and is emitted at an inclination angle Φ ₀ . Here, since Φ ₀ = Φ _{1, the} diffracted light DF enters the interferometer 100. The diffracted light DF incident on the interferometer 100 is reflected by the beam splitter 102 and incident on the reflector 104.

  Next, the diffracted light DF is reflected by the reflecting plate 104 and enters the imaging device 103. At this time, the diffracted light DF and the reference light RF cause interference. An image generated by the interference between the diffracted light DF and the reference light RF is taken by the imaging device 103. The operation and effect are the same as in the previous embodiment.

  The embodiments of the optical disk surface evaluation method and the evaluation apparatus according to the present invention have been described above, but are not limited to those disclosed above, and can be appropriately changed within the scope of the present invention. For example, instead of inclining the interferometer 100 with respect to the substrate 150, the substrate 150 may be inclined.

It is the schematic which shows the evaluation apparatus of this invention. It is an example of the interference fringe observed with the evaluation apparatus of this invention. It is an example of the interference fringe observed with the evaluation apparatus of this invention. It is the schematic for demonstrating the method to make the incident angle of measurement light and the output angle of diffracted light correspond. It is the schematic which shows another example of the evaluation apparatus of this invention. It is the schematic for demonstrating the problem of the evaluation method using the conventional interferometer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Interferometer 101 Light source 102 Beam splitter 103 Image pick-up device 104 Reflector 150 Optical disk board 151 Rotation mechanism

Claims (3)

In the method for evaluating the surface of an optical disc having a substrate with a spiral guide groove formed on one side,
A light source for generating measurement light, a beam splitter for reflecting a part of the measurement light emitted from the light source and transmitting the others and splitting the reflected light and reflecting the diffracted light returned from the substrate; An imaging device that captures interference fringes formed by causing the diffracted light and a part of the measurement light to interfere with each other, and a part of the measurement light or the diffracted light reflected by the beam splitter as the imaging device Using an interferometer having a reflector that reflects toward
Irradiating measurement light with the optical axis of the interferometer inclined with respect to the surface of the substrate,
A method for evaluating the surface of an optical disc, wherein the inclination of the optical axis of the interferometer at this time is the same as the inclination angle of the optical path of the diffracted light. The tilt angle of the optical axis of the interferometer with respect to the virtual perpendicular of the substrate is Φ ₀ , the tilt angle of the optical path of the diffracted light with respect to the virtual perpendicular of the substrate is Φ ₁ , the distance between the guide grooves of the substrate is P, When the wavelength is λ,
Φ ₀ = Φ ₁ = sin ⁻¹ (nλ / 2P)
(N is the order of diffracted light)
The surface evaluation method for an optical disc according to claim 1, wherein In the surface evaluation apparatus for an optical disc having a substrate on which a spiral guide groove is formed on one surface,
A light source for generating measurement light, a beam splitter for reflecting a part of the measurement light emitted from the light source and transmitting the others and splitting the reflected light and reflecting the diffracted light returned from the substrate; An imaging device that captures interference fringes formed by causing the diffracted light and a part of the measurement light to interfere with each other, and a part of the measurement light or the diffracted light reflected by the beam splitter as the imaging device An interferometer having a reflector that reflects toward the
The interferometer is installed such that the optical axis is inclined with respect to the surface of the substrate, and the inclination angle of the optical axis of the interferometer with respect to a virtual perpendicular extending from the surface of the substrate is Φ ₀ , and the virtual angle extending from the surface of the substrate When the tilt angle of the optical path of the diffracted light with respect to the perpendicular is Φ ₁ , the distance between the guide grooves of the substrate is P, and the wavelength of the measurement light is λ,
Φ ₀ = Φ ₁ = sin ⁻¹ (nλ / 2P)
(N is the order of diffracted light)
An apparatus for evaluating the surface of an optical disc, wherein

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