JPH0729214A - Disk for evaluating recording spot diameter - Google Patents

Abstract

PURPOSE:To exactly and easily measure the microspot diameter focused on a master disk by observation of a transmitted light quantity by forming sectorial groove patterns, of which the groove depth has the value half the recording laser wavelength and changes continuously and stepwise in the radial direction of the disk to be evaluated. CONSTITUTION:The disk 1 to be evaluated is moved by a feed motor 3 and is fixed onto a turn table 5 rotated by a spindle motor 4. A recording lens 6 is focused at a focal position. The disk 1 is rotated at a fixed speed and is irradiated with a recording laser beam 7. The light is then observed with an oscilloscope 10 by a photodetector 8 in the lower part of the disk 1 and an amplifier 9. Since the groove patterns 2 are sectorial, the groove width is continuously changed with respect to the laser point if the disk 1 is radially moved. Then, the laser spot diameter condensed to the groove patterns is exactly and easily measured by the transmission intensity of the laser beam from the radial position of the disk 1 and the groove width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc for measuring and evaluating a recording spot diameter of an optical disc master recording device.

[0002]

2. Description of the Related Art CD (Compact Disc), L
The pits of read-only type optical discs such as D (Laser Disc) and the pre-grooves of write-once / rewritable type optical discs are formed by irradiating the glass master coated with photoresist with a laser beam and then developing the pits. -A groove pattern is formed. The shape of the pits, grooves, etc. is determined by the recording power, recording spot diameter, development time, etc. In particular, it is easier to reduce the recording spot diameter in order to record pits with submicron size stably. realizable.

Generally, it is condensed by an objective lens for recording 1
The spot diameter defined by / e ² intensity is 0.82 × (λ /
NA) can be approximated. (Λ: recording wavelength, NA: numerical aperture of objective lens) In recording on an optical disk, an objective lens with an NA of about 0.9 and an argon laser (λ = 457.9 nm)
Is often used as a light source, and the recording spot is about 0.
It has an extremely small diameter of 42 μm. Actually, in the optical path of the recording apparatus, the beam diameter incident on the objective lens is enlarged to about 2 to 3 times the effective aperture, and therefore, when the optical axis of the objective lens and the optical axis of the beam are deviated, the focal point is , And the spot diameter becomes larger than the theoretical value.

Therefore, even if the appropriate recording power is constant, the recorded pit / groove shapes will be different each time. As described above, in the optical disc master recording apparatus, since the measurement / evaluation of the focused spot diameter is required, most of the measurements have been performed by the knife edge method or the magnified observation method of the conjugate image.

FIG. 5 (a) is a schematic view of a conventional example and shows a schematic view of the knife edge method. In this method, a driving mechanism for moving the knife edge 11 in the horizontal and vertical directions and a means for accurately calibrating the respective movement amounts, or a photodetector 12, an amplifier 13, and a light receiving output arranged at opposite positions are used. Differentiation circuit 14 for differentiating the spot diameter
Etc. are required. FIG. 5B is an output waveform diagram in the knife edge method of FIG. 5A and shows the output waveform of the amplifier 13 and the output waveform of the differentiating circuit 14. Then, the spot diameter is measured by the movement amount indicated by X '.

In the case of the magnified observation method of the conjugate image, as shown in the schematic view of the spot monitor measuring method of FIG. 6, a beam splitter 17 and a mirror 18 are arranged on the incident optical path from the laser light source 15 to the disk master 16. ing. Then, after the reflected light flux from the surface of the disk master 16 is branched, a conjugate image of the spot on the disk master 16 is formed by the condenser lens 20 having a focal length f2 longer than the focal length f1 of the recording lens 19. This conjugate spot image is observed and measured by a high-magnification microscope composed of the objective lens 21 and the eyepiece lens 22.

[0007]

However, the knife edge method has the drawbacks that the above-described measuring mechanism and device are required, and that the pattern accuracy of the knife edge affects the measuring accuracy. Further, also in the magnifying observation method of the conjugate image, it is necessary to dispose a new optical path different from the recording optical path. Since it is very difficult to accurately align the optical axes of the condenser lens used in these optical paths, the objective lens in the microscope, and the eyepiece lens, there is a drawback that an image including aberration is observed. In either method, the actual spot diameter condensed on the master during recording is accurately measured,
It has the drawback that it cannot be evaluated.

[0008]

Therefore, in the present invention, in a disk used for measuring or evaluating the recording laser spot diameter of an optical disk master recording apparatus, the groove depth is recorded on a transparent disk-shaped substrate having a flat surface. It has a value of 1/2 the wavelength of the laser and is 0.1 to 1.
It is characterized in that fan-shaped groove patterns whose groove width changes continuously or stepwise at 0 um are arranged radially from the substantially center of the substrate to the outer periphery.

[0009]

When laser light is applied to a substrate (a substrate having a phase structure) having grooves or pits on its surface, a phase difference φ is generated wavewise, and its transmission intensity is expressed as a cos function (φ = 2π
d / λ) A minimum value is obtained in a cycle of d = λ / 2. That is, when a recording laser of 457.9 nm argon laser is used, the transmission intensity becomes minimum at a groove depth of 229 nm. Furthermore,
When the focused beam spot has a Gaussian distribution intensity, the groove width that causes a phase difference is 1 of the beam spot diameter.
It is well known that it becomes a minimum at / 3.

That is, in the present invention, since the groove depth is constant at λ / 2, it can be seen that the intensity of the recording laser light transmitted from the focused disk surface changes in accordance with the groove width. Therefore, by confirming the radial position of the disc and its groove width in advance, the spot diameter focused on the disc master pattern can be easily measured by the intensity of the laser transmitted light.

[0011]

The present invention will be described in detail below. Figure 1
FIG. 3A is a plan view and an essential part cross-sectional view of an evaluation disk according to an embodiment of the present invention. In the figure, a groove pattern 2 is recorded on an evaluation disk 1 having a transparent disk-shaped parallel plane. The groove pattern 2 is fan-shaped and its depth is 1/2 of the recording laser wavelength λ. The evaluation disks 1 are arranged radially from the approximate center to the outer circumference. Also, the usual laser spot diameter is about 0.3 to 3.0 μ.
Since it is m, the groove width that causes a phase difference in the recording laser is about 0.1 to 1.0 μm. Therefore, the width of the fan-shaped groove pattern is about 0.1 μm at the innermost circumference and 1.0 μm at the outermost circumference. FIG. 2 is a plan view of an evaluation disk according to another embodiment of the present invention. As shown in the figure,
There may be several groove patterns in which the groove width changes stepwise. The width of the fan-shaped groove pattern may be wide on the inner circumference and narrow on the outer circumference of the evaluation disk.

Next, a method for producing the evaluation disk of the present invention will be described below. A photoresist is applied to a glass disk having a thickness of about 1.2 mm to a thickness of about 240 nm and baking is performed. The disk after baking changes the exposure amount and the exposure position in the radial direction by the recording device or the like described in the present invention. The changing direction is from the inner circumference to the outer circumference or from the outer circumference to the inner circumference. The exposure method may be an electron beam drawing apparatus other than the above,
Further, any method such as exposing several patterns as shown in FIG. 2 may be used. After exposure, development processing,
Baking. The "film slip" thickness generated during development can be subtracted to create a groove pattern of about 230 nm.
As another preparation method, a photomask may be prepared in advance, and etching may be performed after exposure.

Next, a method for measuring and evaluating the spot diameter using the above evaluation disk will be described. FIG. 3 is a configuration diagram showing an example of a spot diameter measurement / evaluation apparatus. The operation procedure can be performed in almost the same way as the master recording. That is, the evaluation disk 1 of the present invention is moved by the feed motor 3, fixed on the turntable 5 rotated by the spindle motor 4, and the recording lens 6 is focused at the focal position. The evaluation disk 1 is rotated at a constant speed, the recording laser beam 7 is irradiated, and the transmitted light intensity is observed by the oscilloscope 10 or the like by the light receiving element 8 and the amplifier 9 arranged below the evaluation disk 1.

At this time, since the groove pattern 2 arranged on the evaluation disk 1 is fan-shaped, the groove width can be continuously changed with respect to the laser spot by moving the evaluation disk 1 in the radial direction. Therefore, the diameter of the laser spot focused on the groove pattern 2 can be accurately and easily measured from the radial position of the evaluation disk 1 and the groove width that can be confirmed in advance, by the transmission intensity of the laser light. FIG. 4 is a characteristic diagram of the transmitted light intensity, which is an example of the output voltage at each point on the evaluation disk 1. At the point B on the groove pattern 2 arranged in advance on the evaluation disk 1, a case is shown in which the pattern width of the groove pattern 2 and the 1/3 width of the laser spot diameter substantially match. At this time, the diffraction effect is large and the output voltage is minimum.

Position of recording lens 6, that is, evaluation disk 1
By moving the position in the radial direction, the radial position having the minimum value is confirmed. By measuring the groove width corresponding to the radial position in advance, the spot diameter can be measured as a value about three times the groove width at the radial position where the minimum value is obtained.

[0016]

According to the present invention, a new measuring mechanism and device are not required, and a minute spot diameter focused on a rotating master disk in an existing recording apparatus can be measured by observing the amount of transmitted light.
Accurate and simple measurement and evaluation can be performed.

[Brief description of drawings]

FIG. 1 is a plan view and a cross-sectional view of a main part of an evaluation disk according to an embodiment of the present invention.

FIG. 2 is a plan view of an evaluation disk according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of a spot diameter measurement / evaluation apparatus according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram of transmitted light intensity according to an embodiment of the present invention.

FIG. 5A is a schematic diagram of a knife edge measuring method in a conventional example. (B) is an output waveform diagram in the knife edge measuring method in (a).

FIG. 6 is a schematic diagram of a spot monitor measuring method in a conventional example.

[Explanation of symbols]

 1 Evaluation Disc 2 Groove Pattern 3 Feed Motor 4 Spindle Motor 5 Turntable 6,19 Recording Lens 7 Recording Laser Light 8 Photodetector 9 Amplifier 10 Oscilloscope 11 Knife Edge 12 Photodetector 13 Amplifier 14 Differentiation Circuit 15 Laser Light Source 16 Disc Master 17 Beam splitter 18 Mirror 20 Condenser lens 21 Objective lens 22 Eyepiece

Claims (2)

[Claims] 1. A disk used for measuring or evaluating a recording laser spot diameter of an optical disk master recording apparatus, wherein the disk is a transparent disk-shaped substrate having a flat surface with a groove depth of the wavelength of the recording laser. A fan-shaped groove pattern having a value of 1/2 and having a groove width continuously changing from 0.1 to 1.0 um in the radial direction of the substrate is radially arranged from the substantially center of the substrate to the outer periphery. A disc for evaluating a recording spot diameter, which is characterized in that 2. The recording spot diameter according to claim 1, wherein the groove width widens stepwise at 0.1 to 1.0 um in the radial direction of the transparent disk-shaped substrate having a flat surface. Evaluation disk.