JPH04184729A - Optical recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To form the trenches and pits of an optical recording medium used with a short wavelength light without employing an ultraviolet laser cutting machine by a method wherein a laser beam is moved with a pitch less than twice the width of the part of a photoresist layer which is exposed by the laser beam. CONSTITUTION:A photoresist layer 107 is applied to a substrate 101 having a flat-lapped surface and the photoresist layer 107 is exposed by a laser beam to form tracks for holding information. At that time, the laser beam is moved with a pitch less than twice the width of the part of the photoresist layer 107 which is exposed by the laser beam and then the exposed parts are removed by development or the non-exposed parts are removed to form trenches on the substrate 101. Through one or more transcription processes, an optical recording medium substrate having the trenches as the tracks for holding information is formed. With this constitution, an optical recording medium which facilitates recording, reproducing and erasing with a short wavelength light can be obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to marks on a medium for track following control of an optical recording medium that uses light to reproduce, record, or erase information, and its manufacture. It concerns the method.

[Prior art] When reproducing information from optical recording media currently in use,
Alternatively, when recording information on a medium or erasing information on a medium, in order to control the light focusing spot for recording and reproduction to follow the track on which information is recorded, a guide groove formed on the medium is used. The method involves adjusting the position of the spot while capturing the intensity of the diffracted light, and synchronizing two pits (wobble pits) that are perpendicular to the track and shifted in opposite directions at regular intervals along the track. The method used is to form pits (synchronous pits) on the medium and adjust the spot position while monitoring the influence of the wobble bit on the reflected light from the medium while taking timing with the synchronization bit. . These methods are collectively called track servo, the former method is called continuous track servo, and the latter method is called sampling track servo.

The surface shape of the optical recording medium for performing these track servos is based on the ISO/IEC-JTCDI of the International Organization for Standardization.
S10089, and FIGS. 8 and 9 show enlarged views of the surface of the optical recording medium for performing two types of track servo.

The method of forming these grooves and pits on an optical recording medium is to apply photoresist to a glass original plate, expose it to light using a laser cutting machine, develop it, make the surface conductive with a metal film, and then plate it with metal. This is then peeled off from the original plate to create a stamper, and transferred from this stamper onto plastic or the like. An optical recording medium is produced by forming a reflective film, a recording film, and a protective film on the substrate.

[Problems to be Solved by the Invention] In order to improve the recording density of an optical recording medium, the wavelength of light used for recording and reproduction is shortened. Currently 78
Semiconductor lasers with wavelengths from 0 nanometers to 830 nanometers are used as light sources, but if we use a laser with a wavelength of about 400 nanometers, which is half this, the recording density will double in the track direction, and the track spacing will also increase. By halving this, it is possible to increase the total density by four times. The current 780 nanometers, 830 nanometers
Laser cutting machines that use nanometer light to create grooves and pits on optical recording media use laser wavelengths on the order of 400 nanometers. Therefore, when the wavelength of light used for recording and reproducing optical recording media is shortened, the wavelength of the laser cutting machine must also be shortened. However, if the currently used wavelengths were to be made shorter, the ultraviolet light region would be used instead of visible light. However, when using ultraviolet rays, the prisms, lenses, modulation elements, etc. necessary to construct a laser cutting machine are either extremely expensive or impossible to do using the same principle.

Therefore, the present invention solves the drawbacks of the prior art and provides a method for forming grooves and pits in an optical recording medium using short wavelength light without using an ultraviolet laser cutting machine, and an optical recording medium obtained thereby. The purpose is to provide.

[Means for solving the problem] In a method of manufacturing an optical recording medium that uses light to reproduce, record, or erase information, a photoresist is coated on an original plate whose surface is processed to be flat, and a laser beam is applied. When exposing the photoresist using a laser beam to form tracks that hold information, the laser beam is moved at a pitch that is less than twice the width of the photoresist exposed by the laser beam, and then the exposed area is developed. an optical recording medium in which grooves are formed on the original plate by removing the parts that have not been exposed to light, and the grooves are used as tracks for holding information by passing through at least one transfer process. It is characterized by forming a substrate, and forming a reflective film, a recording film, a protective film, etc. on the substrate.Furthermore, when forming a track that holds information, a laser beam is applied to the track at regular intervals. The photoresist is made to meander in a direction perpendicular to the photoresist, and the irradiation of the laser beam is stopped at regular intervals to form an unexposed portion of the photoresist, and then the exposed portion is removed by a development process, or the unexposed portion is removed. By removing grooves, grooves are formed on the original plate, and by passing through at least one transfer process, a substrate for an optical recording medium is formed, and a reflective film, recording film, protective film, etc. is formed on the substrate. It is characterized by forming.

[Example] FIG. 1 shows a method of manufacturing an optical recording medium according to the present invention.

Below, a method for manufacturing the substrate of this optical recording medium and an example of an optical recording medium using the same will be described.

Example 1: Approximately 6 layers of photoresist are applied to a disk-shaped glass original plate 101.
Apply 0 nanometers. This is the state of 102. After baking, exposure is performed using a laser cutting machine (103). In laser cutting, a glass original plate is rotated at a constant rotation rate, and a laser beam using a He-Cd gas laser is focused on the photoresist and continuously irradiated. I shifted it one by one. After exposure, the photoresist is developed (104) and heat treated again.
The surface is subjected to conductive treatment by sputtering, nickel is plated thereon (105), and the nickel plating layer is peeled off from the glass original plate to produce a standber (106). Next, this standber was attached to an injection molding machine, and a substrate for an optical recording medium was created using polycarbonate resin. FIG. 2 is an enlarged view of the recording surface side of this substrate. The depth of the groove is approximately 30 nanometers at 203 in the figure, and the width is approximately 0.6 micrometres at 204 in the figure. In order to use this substrate as an optical recording medium, a recording layer, a protective layer, a reflective layer, etc. are formed on the side with the grooves.

The method of applying track servo to the optical recording medium of this embodiment is the continuous track servo method described above. In the optical recording medium of this embodiment, a push-pull method can be used in which the tracking error is extracted from the difference between the first-order and minus-first-order diffraction components of the reflected light from the medium due to the grooves. Further, in this embodiment, the track pitch can be made very narrow to 0.8 micrometers.

FIG. 5 shows the results of measuring the relationship between the groove depth of the optical recording medium according to the present invention and the tracking error signal using a laser with a wavelength of 415 nanometers. From this figure, it can be seen that the groove depth is not equal to the wavelength of the laser in the substrate of the optical recording medium, and is preferably approximately 1/4 or less.

Example 2: In the laser cutting process of Example 1, one revolution is divided into regular intervals, exposure is interrupted for a minute distance, and after a certain period of time, the focused spot is radially spaced 0. It was vibrated 2 micrometers at a time. A schematic diagram thereof is shown in FIG.

In this figure, one round is divided into four for convenience, and only one round is shown, but in the actual embodiment, the round is divided into 1024 parts, and exposure is further performed in a spiral manner. An optical recording medium was produced from this original plate in the same manner as in Example 1. FIG. 3 shows an enlarged view of the recording surface of this optical recording medium. 301 corresponds to a track, 302 a synchronization mark, and 303 a servo mark for detecting a tracking error.

The tracking servo for the optical recording medium in the present invention is based on the I SO/I EC-J TCDIS1 described in the prior art.
A method similar to format B in 0089, that is, a sampling servo method can be used. In other words, the laser beam is 301 in Figure 3.
When passing through the region, a waveform as shown in FIG. 6 is obtained from the signal reproducing section of the recording device. 60 in Figure 6
1 is a clock signal for synchronization, and 602 is a servo mark signal for measuring the deviation from the center of the track. A track error signal can be generated by sample-holding the two peaks of the signal 602 according to the sampling timing extracted from the clock signal and extracting the difference. Track servo is performed based on this track error signal.

The track pitch of the optical recording medium using the manufacturing method of this example can be significantly reduced compared to the method of recording servo marks using pits, such as format B in ISO/IEC-JTCDIS10089. It is. In other words, in the method of recording servo marks using bits, the size of the pit is determined by the limitations of the laser wavelength of the cutting machine, so in conventional cutting machines, the optical recording medium used for recording and reproducing devices at wavelengths of 400 to 500 nanometers is cannot be manufactured. In the present invention, even if a conventional cutting machine is used, it is possible to create a lock pattern and a servo mark smaller than the laser spot diameter, and the present invention can be applied to an optical recording medium that uses the above-mentioned wavelength band for recording and reproduction.

FIG. 7 shows the relationship between the groove depth and the reproduction amplitude of the clock mark according to the present invention. From this figure, it can be seen that the depth of the groove when used for sample servo is preferably about one-eighth or more of the wavelength inside the substrate of the optical recording medium.

In the first embodiment of the present invention, a case is shown in which the push-pull method is used, but continuous track servo other than the push-pull method, such as a three-beam method, can also be used.

[Effects of the Invention] As described in the examples above, by using the present invention, it is possible to fabricate a substrate for an optical recording medium with higher density using any cutting machine.
By using this substrate, it is possible to obtain an optical recording medium that performs recording, reproducing, and erasing using a wavelength shorter than the conventionally used laser wavelength.

In addition, when the optical recording medium of the present invention is used as a magneto-optical recording medium, it is effective to prevent recording magnetic domains from entering adjacent tracks in both continuous servo systems and sample servo systems, and magneto-optical recording media with small crosstalk can be used. A recording medium can be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a method for manufacturing an optical recording medium according to the present invention. The second plan is an enlarged view of the surface of the optical recording medium manufactured by the manufacturing method of the present invention in Example 1. FIG. 3 is an enlarged view of the surface of an optical recording medium manufactured by the manufacturing method of the present invention in Example 2. FIG. 4 is a schematic diagram showing the timing of laser exposure in the manufacturing method of the present invention in Example 2. FIG. 5 is a diagram showing the relationship between the push-pull error signal and the groove depth of the optical recording medium in Example 1. FIG. 6 is a reproduced signal diagram when the area shown in FIG. 3 is reproduced by optical pickup. FIG. 7 shows the amplitude of the synchronization mark signal in Example 2,
FIG. 3 is a diagram showing the relationship between groove depths of optical recording media. FIG. 8 is an enlarged view of the surface of an optical recording medium using conventional continuous servo. FIG. 9 is an enlarged view of the surface of an optical recording medium using the conventional sample servo method. 901, , Synchronous focus 902, Wobble bit 903,,, ) Rack and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki and 1 other person Fig. 1 Fig. 2 Fig. 3 Fig. 4 Figure 5 Figure 6 Desert depth [X wavelength]: nL! Refractive index of substrate Fig. 7

Claims (4)

[Claims] (1) In a method for manufacturing an optical recording medium that uses light to reproduce, record, or erase information, a photoresist is applied onto an original plate whose surface has been processed to be flat, and the photoresist is removed using a laser beam. When exposing the photoresist to form a track that holds information, the laser beam is moved at a pitch that is less than twice the width of the photoresist exposed by the laser beam, and then the exposed portion is removed by a development process. Alternatively, grooves are formed on the original plate by removing the unexposed portions, and a transfer process is performed at least once to form a substrate of an optical recording medium in which the grooves serve as tracks for holding information. 1. A method for manufacturing an optical recording medium, which comprises forming a reflective film, a recording film, or a protective film on the substrate. (2) In the optical recording medium produced by the method of claim 1, the depth of the groove forming the track is one-fourth the wavelength in the substrate of the optical recording medium of a laser beam used for recording, reproduction, or erasing. An optical recording medium characterized in that: 1 or less. (3) In the optical recording medium produced by the method of claim 1, the grooves forming the tracks meander in a direction perpendicular to the tracks at regular intervals, and discontinuous portions are formed at regular intervals; An optical recording medium characterized in that the depth of the groove is one-eighth or more of the wavelength in the substrate of the optical recording medium of a laser beam used for recording, reproduction, or erasing. (4) When a photoresist is applied onto an original plate whose surface has been processed to have a flat surface and a laser beam is used to expose the photoresist to form tracks that hold information, the laser beam is applied at regular intervals. , the photoresist is made to meander in a direction perpendicular to the track, and the irradiation of the laser beam is stopped at regular intervals to form a portion where the photoresist is not exposed to light, and then the exposed portion is removed by a development process or is not exposed to light. forming a groove on the original plate by removing the removed portion, and forming a substrate of an optical recording medium by passing through at least one transfer process;
4. The method of manufacturing an optical recording medium according to claim 3, further comprising forming a reflective film, a recording film, or a protective film on the substrate.