JP2000242975A - Optical disk and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rewritable optical disk with small noise in which an enough C/N ratio can be obtd. SOLUTION: This optical disk has at least a reflection film, recording film and dielectric film formed in this order on a substrate where grooves/pits are formed, and recording and reproducing are performed through the dielectric film side. Grooves are formed in such a manner that when the groove 1 has the depth D, the opening width of the groove at D-5 nm height from the groove bottom is 250 to 350 nm, the width of the groove bottom is 30 to 150 nm, and the opening width at D/2 height is ((a+b)×0.85)/2 to 1.5×b. The disk can be produced by using a stamper which is produced by applying a photoresist on a glass master disk, irradiating the resist with laser light to form a groove/pit pattern, and heating the master disk to a temp. higher than the softening point of the photoresist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical disk, and more particularly to an optical disk for recording and reproducing by irradiating light from a recording film formed on a substrate and a method of manufacturing the same.

[0002]

2. Description of the Related Art At present, optical discs capable of recording information at high density are used for audio, images, computer memories, and the like. In recent years, there has been a demand for a higher-density optical disk compatible with multimedia.

At present, an optical disk which is put to practical use performs recording / reproduction by using a beam spot obtained by narrowing a laser beam having a wavelength of 780 to 650 nm by a lens having a numerical aperture of about 0.5. The beam spot needs to be smaller.

The diameter d of a beam spot is represented by d = λ / NA where λ is the wavelength of the laser and NA is the numerical aperture of the lens. To reduce the beam spot, the laser wavelength must be reduced or the lens The numerical aperture may be increased. However, short-wavelength lasers that can be used for recording and playback of optical disks have not yet been put to practical use, and increasing the numerical aperture of the lens reduces the depth of focus of the lens system. Since a control system for keeping the lens size is complicated, a lens having an NA of about 0.6 is the largest in practical use.

On the other hand, a solid immersion lens (So
A method using a lid immersion lens (for example, Applied Physics Letter (Appl. Phys. Lett.), vo.
l. 68, p. 144 (1996)). According to this method, assuming that the refractive index of the lens is n, and a hemispherical solid immersion lens is used, the beam spot diameter is d =
λ / (n × NA), super hemisphere (Super Spher)
ical) When a solid immersion lens is used, d =
λ / (n ² × NA), which are 1 / n and 1 / n ² times that of a conventional lens, respectively.

However, the beam spot has such a small size only in the near field (near field) of the solid immersion lens, and when used for recording / reproducing on an optical disk, the distance between the lens and the recording film is changed by a laser.波長 wavelength or less. Therefore, in the conventional optical disk, the recording film is irradiated with the laser beam through the transparent substrate, but in the optical disk using the solid immersion lens, it is necessary to irradiate the laser beam from the side of the recording film formed on the substrate.

Generally, as a rewritable optical disk, a groove serving as a guide groove for guiding an optical pickup for recording and reproduction is formed in a spiral or concentric shape, and information is recorded on a land between adjacent grooves. ,
So-called land recording type optical disks are widely used. The land recording type optical disk has a track pitch of 1.1 μm and a groove width of 0.4 μm even at a high density.

In an optical disk using a solid immersion lens, the recording and reproducing beam spots are about
A disk having a track pitch of 0.5 μm or less is being studied because it can be set to / 2. In order to make the track pitch 0.5 μm or less in the same groove and land shape as the conventional one, the groove width is also 以下 or less of 0.4 μm, that is, 0.2 μm.
m or less. However, an exposure apparatus using an Ar laser or a Kr laser having a wavelength of 351 nm, which is the shortest wavelength currently in practical use, an objective lens having a practically maximum numerical aperture of 0.90, and a high-resolution photoresist are used. However, it was difficult to form a groove having a width of 0.2 μm or less by a normal exposure / development method.

Hitherto, several methods have been proposed for miniaturizing a pattern formed on an optical disk without shortening the wavelength of a laser beam. For example, JP-A-1-31
No. 7241 discloses a method of improving the γ characteristic of a photoresist by forming a hardly soluble layer with a developing solution on the surface of a photoresist before exposure, and Japanese Patent Publication No. 4-11024 discloses a method of performing fine development by performing development in two stages. There has been proposed a method that enables formation of a simple pit.

However, in these methods, since the photoresist surface is further dissolved and then further developed, there is a possibility that a problem occurs in that the land surface and the groove wall surface are roughened. It is transferred to the substrate and becomes a noise when reproducing the recording signal, which has an adverse effect.

Therefore, it has been difficult to manufacture a conventional groove or land having a track pitch of 0.5 μm or less.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and is intended to reproduce and reproduce data on an optical disk having a track pitch of 0.5 μm or less, which performs recording and reproduction using a solid immersion lens. It is an object of the present invention to provide an optical disc with less noise at the time and a sufficient reproduction signal.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on the shapes of the grooves and lands, and as a result, the edges of the grooves and lands formed on the substrate have been smoothed. It has been found that the noise generated at the edge portion is reduced by adopting a simple shape, and the noise generated at the groove bottom is reduced by keeping the photoresist from remaining at the bottom width. Thus, the present invention has been completed.

That is, according to the present invention, at least a reflection film, a recording film, and a dielectric film are formed on a surface of a substrate on which a groove serving as a guide groove and a pit on which an information signal is recorded is formed. In an optical disk formed and recorded or reproduced from the dielectric film side, when the groove formed on the substrate has a groove depth D, the opening width a at a position D-5 nm from the groove bottom,
Groove bottom width b and opening width c at the position of D × １ ／
Satisfies the following relationship: a: 250 nm to 350 nm b: 30 nm to 150 nm c: ((a + b) × 0.85) / 2 to 1.5 × b When manufacturing such optical discs, a laser beam is irradiated onto a glass master coated with photoresist to expose the grooves and pit patterns, and the exposed or unexposed portions of the photoresist are dissolved and removed with an alkaline aqueous solution to remove the grooves. And a method for manufacturing an optical disk, characterized by using a stamper obtained from a step of heating the master to a temperature higher than the softening point of a photoresist after forming pits.

Hereinafter, the present invention will be described in detail.

As described above, the optical disk of the present invention
The groove has a special feature in its shape. That is, assuming that the groove depth is D, D
The opening width a at the position of −5 nm is 250 nm to 350 n.
m, preferably 270-320 nm in that the intensity of the reproduced signal can be further obtained, and the groove bottom width b is 30 nm-1.
The opening width c at a position of 50 nm, preferably 80 to 150 nm, and D × １ ／ in terms of less noise during reproduction, is ((a + b) × 0.85) / 2 to 1.5 × b. It is characterized by the following.

The depth of the groove is preferably 50 nm or more in order to obtain a sufficient tracking signal, and is preferably 100 nm or less in order to form a groove having the above-mentioned shape by a conventional exposure technique.

Hereinafter, the present invention will be described with reference to the drawings. The present invention is not limited to the following examples.

FIG. 1 shows a cross section of an optical disk of the present invention, and FIG. 2 shows a cross section of a conventional optical disk. In these drawings, the substrate portion of the optical disk is schematically enlarged, and in an actual optical disk, a reflection film, a recording film, a dielectric film, and the like are formed on such a disk substrate.

In a conventional optical disk, as shown in FIG. 2, the groove is formed in a V-shape. In such a conventional optical disc, the width of the groove corresponds to the spot diameter of the laser beam for laser cutting. Therefore, in order to reduce the track pitch in the same shape as the conventional one as shown in FIG. It is necessary to reduce the spot diameter.
However, as described above, it is very difficult to reduce the spot diameter of the laser beam, and therefore, it has been difficult to increase the recording density in the conventional optical disk substrate shape.

On the other hand, as shown in FIG. 1, in the optical disk of the present invention, the groove width is almost equal to that of the conventional optical disk, and the track pitch is narrow, so that the land becomes narrower than the conventional optical disk. However, the edges of the grooves and lands are smooth and the bottom is flat. Due to such a shape, there is little noise and sufficient S
/ N can be obtained.

The optical disk of the present invention is suitable for narrow pitch applications, but has a track pitch of 0.3 to 0.5 μm.
m is preferred. The optical disk as described above, for example, irradiates a groove or a pit pattern by irradiating a laser beam onto a glass master coated with a photoresist, and dissolving and removing the photoresist in an exposed portion or an unexposed portion with an alkaline aqueous solution. After forming the grooves or pits, the master can be obtained from a substrate obtained by using a stamper obtained through a process including a process of heating the master to a temperature higher than the softening point of the photoresist.

Next, a method for manufacturing the optical disk of the present invention will be specifically described.

To manufacture the optical disk master of the present invention,
First, a photoresist layer is formed on a precisely polished glass substrate. Here, the thickness of the photoresist layer is formed to have a desired groove depth, and is preferably 50 to 100 nm. Further, a positive photoresist is usually used, but a negative photoresist can be used.

Next, the formed photoresist layer is irradiated with a laser beam, cut, and developed to form grooves and pits. In the optical disc of the present invention, since the groove bottom width is the bottom width after development, the development process is performed so as to have a desired groove bottom width.

Thereafter, the master on which the groove is formed is subjected to a heat treatment. The heating conditions vary depending on the heating method, heating time, photoresist, and the like, but are higher than the softening point of the photoresist, preferably 5 to 20 from the softening point of the photoresist.
Perform at 20 ° C. higher temperature for 20-60 minutes. This process makes the edges of the grooves and lands smooth.

Thereafter, the master optical disc may be manufactured by the same steps as in the conventional method. That is,
After a conductive thin film made of nickel or the like is formed on the photoresist layer having a gentle edge, an electroforming process is performed to form an optical disk master made of nickel or the like on the photoresist layer. Thereafter, the optical disk master is peeled off from the photoresist layer to complete the optical disk master.

Based on the optical disk master, a resin substrate made of polycarbonate, polymethyl methacrylate, amorphous polyolefin, or the like is manufactured by an injection molding method. In addition, the substrate can be manufactured by a 2P method using an ultraviolet curable resin.

On this substrate, Al, Ag, Au, Cu, T
a reflective film made of a metal such as i, Ni, or an alloy thereof;
A first dielectric thin film made of SiN, SiO, ZnS, or the like;
TbFeCo, GdFeCo, GdTbFeCo, Dy
Magneto-optical recording film made of FeCo, etc., SiN, Si
A second dielectric thin film made of O, ZnS or the like is formed in this order. Further, a protective film made of diamond-like carbon and the like, and a lubricating film made of perfluoropolyether and the like are formed on the film to complete the optical disc.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

A primer (trade name "OA" manufactured by Tokyo Ohka Kogyo Co., Ltd.)
P "), and then a positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name" TSMR-8900D ",
(Softening point: 140 ° C.) Spin coating was performed. Then 95 ° C
Pre-baked on a hot plate for 15 minutes to make the film thickness 85n
m of photoresist master was manufactured.

Next, a cutting machine equipped with an Ar laser having a wavelength of 351 nm and an objective lens having a numerical aperture of 0.90 has a radius of 20 mm to a radius of 6 mm from the photoresist master.
A region up to 5 mm was exposed at a pitch of 425 nm. Then, an inorganic alkali solution (manufactured by Shipley, trade name "Microposit Developer") and ultrapure water are mixed at a volume ratio of 1: 5 and spin-developed with a developing solution to form spiral grooves and pits. After formation, it was post-baked on a hot plate at 155 ° C. for 35 minutes.

Thereafter, 100 nm is formed on the photoresist on which the grooves and pits have been formed by sputtering.
Was formed as a conductive film. Using this Ni conductive film as an electrode, Ni electroforming plating was performed to produce a 0.3 mm thick Ni stamper. Next, after the back surface of the Ni stamper was polished and peeled from the photoresist master, the inner peripheral portion and the outer peripheral portion were punched.

Using the stamper thus manufactured, a polycarbonate resin substrate having a diameter of 130 mm and a thickness of 2 mm was manufactured by injection molding. When the groove shape of this substrate was measured by AFM (atomic force microscope), the groove depth was 80 nm, and the groove depth was 80 nm from the groove bottom.
nm opening width a: 300 nm, groove bottom width b:
The opening width c at a position 40 nm from the groove bottom was 80 nm and the groove width c was 160 nm.

An Al alloy film having a thickness of 50 nm is formed as a reflective film on the substrate by DC sputtering, and then a first dielectric layer made of SiN having a thickness of 10 nm is formed in a mixed atmosphere of Ar and N _2. It was formed by a reactive RF sputtering method using a Si target. Subsequently, a 20 nm-thick Tb
_A magneto-optical recording layer of ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ was formed by a DC simultaneous sputtering method using a Tb target and an Fe ₉₀ Co ₁₀ target. On top of this, a 25 nm-thick SiN
A second dielectric layer is formed in the same manner as the first dielectric layer, and a diamond-like carbon (DLC) layer having a thickness of 15 nm is formed in a mixed atmosphere of Ar and CH _4.
It was formed by a reactive RF sputtering method using a target. As a lubricating layer, piperonyl-modified perfluoropolyether was applied to a thickness of 0.3 nm from a perfluoropolyether-based solvent solution by a dip method on these films.

The recording / reproducing characteristics of the optical disk manufactured by the above process were evaluated using a tester in which a solid immersion lens having a laser wavelength of 650 nm and an effective numerical aperture of 1.4 was mounted on a flying slider. The flying slider flies above the surface on which the thin film is formed at a height of about 100 nm, and the laser is incident from the thin film side and is reflected and reproduced on the thin film side. The tester used for the evaluation performs a tracking servo by a push-pull method, and detects a magneto-optical signal by a differential optical system.

The conditions for evaluating the recording / reproducing characteristics are as follows.
0 rpm, a recording radius of 45 mm, and a light modulation method of modulating a laser pulse at 19 MHz while changing the laser intensity with an applied magnetic field of 1500 e in an erased state.
A 0 nm mark was recorded. As a result, a C / N ratio of 47.5 dB was obtained.

[0038]

As is clear from the above description, the optical disk of the present invention has a smooth groove and land edges and a flat bottom, so that it has low noise and a sufficient C / N ratio. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of an optical disc of the present invention.

FIG. 2 is a diagram showing a cross section of a conventional optical disc.

FIG. 3 is a diagram showing a cross section of a high-density optical disk having a groove of a conventional shape.

[Explanation of symbols]

 1: Groove 2: Land

Claims (4)

[Claims] 1. An optical disc in which at least a reflection film, a recording film and a dielectric film are formed on a substrate surface on which pits on which grooves and information signals are recorded are formed, and recording or reproduction is performed from the dielectric film side. When the groove formed on the substrate has a groove depth D, the opening width a at the position of D-5 nm from the groove bottom, the groove bottom width b, and the opening width c at the position of D × １ ／. Satisfies the following relationship: a: 250 nm to 350 nm b: 30 nm to 150 nm c: ((a + b) × 0.85) / 2 to 1.5 × b 2. The track pitch of a groove is 0.3 μm.
2. The optical disk according to claim 1, wherein the optical disk has a thickness of about 0.5 μm. 3. The groove depth D is 50 nm to 100 n.
3. The optical disk according to claim 1, wherein m is m. 4. A method of manufacturing an optical disk using a stamper, comprising forming a groove and a pit pattern on a glass master coated with a photoresist and heating the master to a temperature higher than a softening point of the photoresist. A method of manufacturing an optical disk, comprising using a stamper provided.