JP2000242984A - Optical recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium having superior recording and reproducing characteristics even in the case of a minute pitch. SOLUTION: The optical recording medium is obtained by using a stamper produced by forming a thin film of a dielectric such as SiO2, Si3N4 or Al2O3 on a photoresist pattern obtained by exposure and development, forming a metallic stamper by electroforming and then removing the thin film. In the optical recording medium, the pitch P of a continuous groove formed on the substrate is 300-450 nm, the depth D of the groove is >=40 nm and the half-width W of the groove satisfies W/P<=0.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium,
The present invention relates to a magneto-optical recording medium capable of obtaining good recording / reproducing characteristics in a medium having a small groove pitch and a method for manufacturing the same.

[0002]

2. Description of the Related Art Optical recording media are portable recording media capable of large-capacity, high-density recording. Demand is increasing rapidly as rewritable media for storing large-capacity data in computers. Accordingly, higher densification is required.

In an optical recording medium, a guide groove for performing tracking servo is usually provided in a physical shape on a substrate at a position where a laser beam is recorded / reproduced, and recording is performed at a portion where the substrate is convex between the grooves. (Hereinafter referred to as land). Therefore, the larger the land, the larger the mark width to be recorded can be made, and the intensity of the reproduction signal can be increased, and the quality of the reproduction signal can be improved.

However, in order to increase the recording density, it is necessary to increase the information per recording area by reducing the pitch which is the interval between the grooves. For example, the pitch of a commercially available 3.5-inch diameter magneto-optical recording medium is reduced to 1.6 μm for a storage capacity of 128 MB, 1.4 μm for a storage capacity of 230 MB, and 1.1 μm for a storage capacity of 640 MB. Is coming. To increase the density, it is necessary to further reduce the pitch. However, if the pitch is reduced while the groove width remains the same, the width of the land is reduced. Therefore, to reduce the pitch, a narrow groove is required.

On the other hand, the recording density is a laser beam spot size (.about..lamda. / NA) determined by the light source laser wavelength (.lambda.) Of the recording / reproducing apparatus and the numerical aperture (NA) of the objective lens.
Is limited by For example, in the case of the above-mentioned recording / reproducing apparatus for a 640 MB magneto-optical recording medium, the wavelength: 680 nm,
NA: 0.55, and the laser beam spot size is about 1240 nm.

As a means for reducing the laser beam spot size and achieving high density, so-called near-field optical recording, in which an optical head is brought close to a recording film to perform recording and reproduction, has attracted attention (for example, Applied Physics Letter). (Appl. Phys. Lett.), Vol.
p. 141 (1996)). In this recording method, Sol
id Immersion Lens (hereinafter “SIL”)
By using a head and increasing the effective numerical aperture when the SIL is used, the laser beam spot size is reduced, and recording and reproduction at an ultra-high recording density can be realized.

For example, wavelength: 650 nm, effective NA:
In near-field optical recording using an SIL of 1.4, the laser beam spot size is about 460 nm, which is about 37 nm of the laser beam spot size used in the above-mentioned recording / reproducing apparatus for the conventional 640 MB magneto-optical recording medium. %.

As described above, in near-field optical recording using SIL, a laser beam spot size (about 460 n
The groove pitch corresponding to m) is required to be about 400 nm,
Also, from the viewpoint of signal quality, it is necessary to form a narrower groove to obtain a large land. That is, it is necessary to form a finer pattern.

Conventionally, a guide groove formed on an optical recording medium is formed roughly by the following stamper manufacturing process and molding process.

The stamper manufacturing process includes, for example, the following processes.

(1) Exposure by a mastering device to a photoresist master obtained by applying a photoresist to a glass substrate; (2) formation of a resist pattern by development using an alkali developing solution; (3) post-baking of the resist; 4) formation of a metal conductive film by a sputtering method; (5) formation of a stamper by electroforming of metal; (6) polishing of the back surface of the stamper; (7) separation of the photoresist master from the stamper; and (8) residual photo on the surface of the stamper. (9) Punching to adjust the inner and outer circumferences of the stamper to the die diameter of the injection molding machine.

On the other hand, in the molding step, for example, a stamper is set in a mold of an injection molding machine, and a substrate is molded with a polycarbonate resin, and a groove is transferred.

A conventional mastering device having an optical system having a wavelength of 454 nm and an NA of 0.9 is generally used for manufacturing a stamper for a conventional magneto-optical recording medium up to 640 MB. The lower limit was about 300 nm. Further, in order to reduce the width of the groove, the wavelength: 351 n
A mastering device having a UV optical system of m, NA: 0.9 has also been put to practical use. However, at a pitch of 400 nm, the lower limit of the groove width at 50% of the groove depth (half-width at groove) is about 210 nm. The upper limit of the land width (land half width) at 50% of the depth is 190 nm. With this land width, sufficient signal quality could not be obtained even in near-field optical recording with a laser beam spot diameter of 460 nm.

[0014]

In an optical recording medium using a stamper manufactured by a conventional stamper forming method,
When a very small pitch is required as in near-field optical recording using SIL, there is a problem that a land width for recording a signal becomes small and sufficient signal quality cannot be obtained.

The present invention proposes a novel stamper manufacturing method, provides an optical recording medium capable of sufficiently securing a land width even with a minute groove pitch, and further has a near-field having a groove shape suitable for near-field optical recording. It is an object to provide an optical recording medium.

[0016]

In view of the above situation, the present inventors have made intensive studies and, as a result, have invented a stamper manufacturing method for obtaining a sufficient land width at a fine groove pitch. The inventors have invented an optical recording medium capable of obtaining a sufficient reproduction signal in field light recording.

That is, according to the present invention, when the pitch P of the continuous groove formed on the substrate is 300 nm to 450 nm, the depth D of the groove is 40 nm or more, and the half width of the groove is W, W / P is 0.1. 5 or less, and a method of manufacturing an optical recording medium using a stamper,
An optical recording medium using a stamper manufactured by forming a dielectric thin film on a photoresist pattern obtained by exposure and development, forming a metal stamper by electroforming, and removing the thin film. And a method for producing the same.

Hereinafter, the present invention will be described in detail.

In the optical recording medium of the present invention, when the pitch P of the continuous groove formed on the substrate is 300 nm to 450 nm, the depth D of the groove is 40 nm or more, and the half width of the groove is W,
W / P is 0.5 or less. The groove depth is preferably from 40 to 100 nm in terms of stabilization of the tracking servo by the push-pull method utilizing the diffraction effect. The value of W / P is 0.5 or less in order to obtain an excellent reproduced signal. It is preferably 0.3 or more in order to obtain a sufficient diffraction effect.

Such an optical recording medium can be obtained, for example, by the following manufacturing method.

In the conventional method of manufacturing a stamper, a metal conductive film is formed by a sputtering method after post-baking a resist. However, according to the manufacturing method of the present invention, after a post-baking of a resist is performed. Then, a dielectric thin film is formed on the resist pattern. By such a process, a dielectric thin film is laminated on the land surface or the groove surface, but since the dielectric is laminated so as to fill the slope of the groove, the groove width is narrower than the original resist pattern, The land width increases. Also, the decrease in the groove depth is slight.
Since the change in the groove depth due to the formation of the dielectric film is small, it is possible to manufacture a substrate having a groove depth of 40 to 100 nm, which is preferable for stabilizing the tracking servo by the push-pull method.

After forming the dielectric thin film, a Ni conductive film is formed for electroforming, and Ni is electroformed. After polishing the back surface of the stamper after electroforming to make the surface smooth, the photoresist master and the stamper are separated. Since the dielectric thin film remains on the peeled stamper surface,
This film is removed by etching with CF ₄ gas or the like. Since the stamper obtained by this manufacturing method has a wide land width and is formed of the same Ni as the conventional one, it is possible to manufacture a substrate on which the groove pattern has been transferred by injection molding as in the conventional case.

Here, the thin film formed on the resist pattern may be any material that can be removed by etching.
It can be used without particular limitation, for example, SiO ₂ , S
i ₃ is N _4, Al ₂ O _3, or the like can be exemplified, SiO in terms of high etch selectivity between the stamper material (Ni)
₂ is preferred. Further, as the thin film forming method, a sputtering method which is excellent in pattern coverage is preferable. The removal of the dielectric remaining on the surface of the peeled stamper can be performed not only by gas phase etching but also by liquid phase etching using hydrofluoric acid or the like.

When the thickness of the dielectric thin film is too small, the effect of narrowing the groove and increasing the land becomes small, and when the thickness is too large, film peeling due to stress of the film is likely to occur.
It is preferably from 0 to 500 nm, particularly preferably from 200 to 500 nm.
400 nm.

Further, the conductive film for electroforming is not limited to only Ni, but may be Ag or Co.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Examples 1-4 A positive type i-line photoresist (trade name "THMR-ip365" manufactured by Tokyo Ohka Kogyo Co., Ltd.) was formed on a glass substrate having a thickness of 6 mm.
0 ") with a 100 nm-thick photoresist master, and an Ar laser light source having a wavelength of 351 nm and an NA of 0.9.
Exposure is performed at a pitch of 350 nm (Examples 1 and 3) and 400 nm (Examples 2 and 4) using a mastering device having an optical system with an objective lens, and a spiral shape having a groove depth of 80 nm by development with an organic developer. A resist pattern in which a groove was formed was formed.

The photoresist master is post-baked at 120 ° C. for 30 minutes, and a SiO ₂ film having a pitch of 400 nm is formed on the resist pattern by high frequency sputtering.
A 50 nm photoresist master was formed to have a thickness of 200 nm (Examples 1 and 2) and a thickness of 400 nm (Examples 3 and 4), respectively. Subsequently, a Ni film is formed on the SiO ₂ film.
After forming the Ni film to a thickness of 0.3 nm, the Ni film is
A stamper was manufactured by precipitation with a thickness of mm. After polishing the back surface of the stamper while the photoresist master and the stamper were in close contact with each other, the photoresist master and the stamper were mechanically peeled off. After the peeling, SiO ₂ remaining on the stamper surface was removed by reactive etching using CF ₄ gas.
Further, the inner and outer peripheries of the stamper were punched out, set in a mold of an injection molding machine, and injection molded with polycarbonate resin to produce a substrate having a thickness of 2 mm and a diameter of 130 mm.

The groove shape of the substrate thus manufactured was measured by an atomic force microscope (AFM). Table 1 shows the groove half width, land half width, groove depth, and the groove half width / groove pitch ratio obtained by dividing the groove half width by the groove pitch.

[0030] to form a SiO ₂ film on the resist pattern, the land FWHM SiO ₂ film is coated so as to cover the land is a convex portion increases. The reason that the larger the groove width is, the larger the increase of the land half-value width is probably because the larger the groove width is, the higher the covering efficiency on the slope is. Also, the Si to be formed
The larger the O ₂ film thickness, the larger the land half width.

[0031]

[Table 1]

Using these substrates, a magneto-optical recording medium for near-field optical recording was manufactured as described below. On the groove forming surface of the substrate, an Al alloy film (45 nm thick) was used as a reflective layer.
m) was formed by DC sputtering, and then a first protective layer made of SiN was formed by reactive RF sputtering using a Si target in a mixed atmosphere of Ar and N ₂ (film thickness: 10 nm). Next, a magneto-optical recording layer made of Tb ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ was formed by DC simultaneous sputtering of a Tb target and an Fe ₉₀ Co ₁₀ target (film thickness: 20 n).
m). Further, a second protective layer made of SiN is further formed thereon by Ar
And it was formed by a reactive RF sputtering method using a Si target in a mixed atmosphere of N ₂ (film thickness 25 nm). A diamond-like carbon (DLC) layer was formed thereon by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ (film thickness: 15 nm). This D
As a lubricant, a solution of piperonyl-modified perfluoropolyether using a perfluoropolyether solvent was applied as a lubricant to the LC layer to a thickness of 0.3 nm by a dipping method.

The near-field optical recording type magneto-optical recording medium manufactured by the above process is mounted on a flying slider with a SIL having a laser wavelength of 650 nm and an effective NA of 1.4.
The recording and reproduction characteristics were evaluated with a tester. 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 SIL 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 150 Oe in an erased state.
A 00 nm mark was recorded. Table 1 shows the maximum reproduced signal strength (carrier level) and carrier level to noise level ratio (C / N ratio) obtained when recording was performed with different powers.
Is shown.

Comparative Examples 1 and 2 Using the same materials, devices and methods as in Examples 1 to 4,
On a photoresist master, a groove depth of 80 nm with a pitch of 400 nm (Comparative Example 1) or 350 nm (Comparative Example 2)
Was formed.

The photoresist master is post-baked at 120 ° C. for 30 minutes, a Ni film is formed on the resist pattern by sputtering to a thickness of 100 nm, and Ni is deposited to a thickness of 0.3 mm on the Ni film by electroforming to form a stamper. Manufactured. After polishing the back surface of the stamper while the photoresist master and the stamper were in close contact with each other, the photoresist master and the stamper were mechanically peeled off. After peeling, the inner and outer peripheries of the stamper are punched out, set in a mold of an injection molding machine, and injection molded with polycarbonate resin to a thickness of 2 mm and a diameter of 1 mm.
A 30 mm substrate was manufactured.

The groove shape of the substrate thus manufactured was measured by an atomic force microscope (AFM). Table 2 shows the groove half width, land half width, groove depth, and the groove half width / groove pitch ratio obtained by dividing the groove half width by the groove pitch. When manufactured by these known methods, the half width of the groove was 50% or more of the groove pitch.

[0038]

[Table 2]

Using these substrates, a near-field having a reflective layer, a first protective layer, a magneto-optical recording layer, a second protective layer, a DLC layer and a lubricating layer on the substrate in the same manner as in Examples 1 to 4 Table 2 shows the results of manufacturing a magneto-optical recording medium for optical recording and evaluating the recording / reproducing characteristics in the same manner as in Examples 1 to 4.

It can be seen from Comparative Examples 1 and 2 that the reproduction signal intensity is greatly reduced due to the decrease in the land half width.
On the other hand, in the medium obtained in the example, although the groove depth was reduced by 3 to 7 nm as compared with the comparative examples 1 and 2,
There was no problem with the tracking servo by the tester.

In the first embodiment, the carrier level is high even though the half width of the land is smaller than that of the second comparative example because the SiO ₂ film covers the corner of the resist gently on the land. This is probably because the width of the mark has been effectively increased. In addition, the noise level in all of the examples is lower than that of Comparative Examples 1 and 2 by about 1 dBm, which is also considered to be due to the SiO ₂ film covering the corners of the resist gently above the lands. These expectations do not limit the invention in any way.

[0042]

According to the present invention, in a magneto-optical recording medium such as a near-field recording type which requires a fine pitch, light having excellent recording / reproducing characteristics can be obtained by setting the groove half width to 50% or less of the pitch. A recording medium can be provided. In particular,
Even at a groove pitch of 400 nm, a groove half width of 140 nm is obtained, and a land half width of 260 nm is possible.

Claims (2)

[Claims] A pitch of a continuous groove formed on a substrate;
An optical recording medium, wherein the half width W of the groove and the depth D of the groove are represented by the following relationship. P: 300 nm or more and 450 nm or less W / P: 0.5 or less D: 40 nm or more 2. A method for manufacturing an optical recording medium using a stamper, wherein a dielectric thin film is formed on a photoresist pattern obtained by exposure and development, and after forming a metal stamper by electroforming, the thin film is removed. A method for manufacturing an optical recording medium, comprising using a stamper manufactured through the steps of: