JP2002298359A - Optical recording medium and method for recording on the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once optical recording medium having a recording layer made of an organic material even in a short wavelength region near 400 nm so that a high modulation degree can be easily obtained and the dependence on the refractive index (wavelength dependence) of the recording layer can be significantly improved. SOLUTION: In the optical recording medium having a recording layer formed on a substrate having at least pregrooves, the recording part is formed in the grooves of the pregrooves by enlarging the grooves with almost equal increments of the groove bottom width and the groove opening width in the substrate by irradiation of laser light.

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 and a recording method for the optical recording medium.

[0002]

2. Description of the Related Art Optical recording media having a recording layer of an organic material such as a CD-R and a DVD-R have been put to practical use. In these optical recording media, for example, “SPIE Vol.1078 Opti
cal Data Storage Topical Meeting (1989) pp.80-87 "
And "Jpn. J. Appl. Phys. Vol. 31 (1992) pp. 484-49
As described in “3”, the recording portion is formed by expansion (bump) of the substrate, decomposition of the recording layer material, deformation of the reflective layer, and the like. In addition, "Jpn. J. Appl. Phys.
Vol.36 (1997) pp.403-409 ”, the CNR of the reproduced signal
There is a description that (carrier to noise ratio) is correlated with the expansion height and expansion width of the substrate bottom due to recording. Furthermore, "http://search.zdnet.co.jp/magazine/cshop/001
2 / sp3 (ComputerShopper Japan Home Page)
As a recording principle of DR, there is a description that the reflectance of light decreases due to the deterioration of the dye and the material of the substrate. Also, "htt
p: //www.orangeforum.or.jp/j/cdr/cdr_mechanism1.htm
(Official site of the Orange Forum, a corporate organization for disseminating the CD-R / RW standard conforming to the Orange Book), describes the principle of CD-R recording, including substrate deformation and refraction due to decomposition of dyes. There is a description that a recording pit is formed by a change in rate.

On the other hand, as a recording method of an optical recording medium, "Optical disc technology, supervised by Morio Onoe, Radio Engineering, p. 315"
As described above, as a write-once optical disc, a recording method such as a punching type, a phase change type, a bubble type, and a texture type has been proposed. Japanese Patent No. 2710040 discloses that a recording method for obtaining a high degree of modulation in a CD-R optical disk includes forming a bump (expanded portion) on a substrate or forming a deteriorated portion having an optical characteristic on a recording layer. Alternatively, a method is described in which a void is formed at the interface between the recording layer and the reflective layer, fine bubbles are dispersed in the recording layer, or a deteriorated portion of optical characteristics is formed on the substrate. Also, JP-A-8-7275 discloses that
An optical recording medium having a recording layer made of a shape memory resin directly or via a dielectric layer on a transparent substrate is irradiated with a laser beam so as to focus on the vicinity of the interface of the recording layer on the substrate side, so that the shape memory is obtained. A recording method has been proposed in which convex pits are formed by thermally expanding a resin.

Conventionally, in the case of a write-once optical recording medium having a recording layer made of an organic material, the organic material that can be used as the recording layer has very severe restrictions on optical characteristics. This is described, for example, in "Jpn. J. Appl. Phys. Vol. 31 (19
92) pp. 484-493 ”, in order to ensure a high degree of modulation and a high reflectance, it is necessary that the refractive index of the recording layer material is sufficiently high. The reason why the refractive index of the recording layer material needs to be sufficiently high to secure a high degree of modulation is that the refractive index of the recording layer material changes before and after recording due to the decomposition of the recording layer material due to laser beam irradiation. It is said that a phase difference is generated to generate a modulation degree. Therefore, (1) a very large load is applied to the selection of the material for the recording layer, (2) the cost is not reduced when only the materials difficult to synthesize can satisfy the optical characteristics, and (3) a region having a large refractive index is used. (4) It is difficult to develop a write-once optical recording medium having a recording layer made of an organic material in a wavelength region having a very large wavelength dependency and (4) a wavelength region in which it is difficult to increase the refractive index, for example, a wavelength region of 450 nm or less (molecules). Since the extinction coefficient decreases as the absorption wavelength becomes shorter, it is very difficult to achieve a high refractive index in the short wavelength region.) (5) In addition to optical properties, good thermal decomposition properties are required. (Decomposition at a low temperature in a short time). In addition, a write-once optical recording medium using an inorganic material also requires a recording method capable of obtaining good recording characteristics.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording medium having a recording layer provided on a substrate having at least a pregroove, in which a recording contrast (modulation degree) is easily obtained. And a recording method. It is another object of the present invention to provide an optical recording medium and a recording method that improve a large wavelength dependence of recording characteristics, which is a problem specific to a write-once optical recording medium having a recording layer made of an organic material. Furthermore, even when the recording / reproducing wavelength is shortened, for example, when the wavelength is near 400 nm, an optical recording medium and a recording method that can easily realize a write-once optical recording medium having a recording layer made of an organic material are provided. The purpose is to.

[0006]

Means for Solving the Problems As a result of diligent studies, the present inventor has found that an optical recording medium having a recording layer provided on at least a substrate having a pre-groove, wherein a recording portion is formed in a groove of the pre-groove. In an optical recording medium to be used, in a recording method (recording principle) conventionally proposed such as expansion of a substrate (bump), decomposition of a recording layer material, or deformation of a reflective layer, a sufficient refractive index of the recording layer material is required. In order to improve the inability to obtain the recording contrast (modulation degree), a recording method has been newly found in which a sufficient recording contrast (modulation degree) can be obtained without largely depending on the refractive index of the recording layer material. .

In the conventional recording method (recording principle) for a write-once optical recording medium having a recording layer made of an organic material, there were very strict restrictions on the physical property values of the recording layer material. It has been found that the strict restrictions on the physical properties imposed on the recording layer material can be relaxed by the method.

Hereinafter, an optical recording medium of the present invention will be described with reference to the drawings. The groove shape of the substrate in the unrecorded state of the optical recording medium having a pre-groove is, for example, as shown in FIG.
Groove depth (ζ), substrate groove dripping amount (A) and (C−
B), the width of the groove bottom of the substrate (BA), the width of the groove above the substrate (groove opening width) (C), and the track pitch (D).

FIG. 2 is a diagram for explaining a recording method for an optical recording medium according to the present invention. FIG. 2A shows an unrecorded state (however,
Only the substrate is shown). By recording, as shown in FIG. 2B, the width of the groove bottom of the substrate (1) is set to (BA) +
α, a recording method for enlarging the width of the upper part of the substrate groove (groove opening width) to C + β, wherein α ≒ β> 0,
With this recording method, it is possible to easily obtain a high modulation degree.

In the present invention, this recording method is used,
It is characterized in that the groove portions and the inter-groove portions of the pre-groove and the recording layer have substantially the same thickness. Thereby, the dependence of the degree of modulation on the refractive index of the recording layer can be significantly improved. For example, in the case of a write-once optical recording medium having a recording layer made of a normal organic material, the recording layer is formed by spin coating, so that the surface of the recording layer also has an uneven portion reflecting the shape of the pre-groove. However, the thickness of the recording layer in the groove portion is formed sufficiently thicker than the thickness of the recording layer in the inter-groove portion (land portion). Therefore, in the case of an optical recording medium having a reflective layer such as a CD-R or a DVD-R, the unevenness at the interface between the recording layer and the reflective layer is smaller than the unevenness at the interface between the substrate and the recording layer.
Therefore, when the recording / reproducing wavelength is shortened, the refractive index of the organic material is reduced, and the refractive index difference between the substrate and the recording layer is reduced.
The phase change is caused by the unevenness of the interface between the recording layer and the reflection layer. The phase change due to the unevenness of the interface between the recording layer and the reflective layer is smaller than the phase change due to the unevenness at the interface between the substrate and the recording layer. Even if the change in the optical characteristics of the layer material or the change in the groove shape of the substrate is large, a sufficient degree of modulation cannot be obtained. In other words, in an optical recording medium having a pre-groove, since the laser beam must follow the groove, the groove shape (groove width and depth) of the substrate is designed to be such that the laser beam sufficiently diffracts. However, the diffraction index is designed so that diffraction occurs sufficiently in the state where the recording layer is formed. Interference between 0th-order light and ± 1st-order light is used for tracking, but the refractive index of the recording layer decreases. When the difference in refractive index from the substrate decreases, the diffraction effect mainly occurs due to the unevenness of the interface between the recording layer and the reflection layer. Therefore, the diffraction effect is not sufficient, and the change in the optical constant and the groove shape of the recording layer are not sufficient. Even if it occurs, the degree of modulation is reduced.

Therefore, in the present invention, the recording method described above is used as a method for generating a sufficient degree of modulation even when the refractive index of the recording layer decreases and the difference in refractive index from the substrate decreases, and It has been found that it is effective to make the thickness of the recording layer approximately equal to the groove portion and the inter-groove portion of the pre-groove. This method actively utilizes the fact that even if the recording / reproducing wavelength is short, the refractive index of the substrate or the recording layer and the air layer or the reflective layer still have a large refractive index difference. That is, by setting beforehand an interface having a large refractive index difference that causes a phase change (an uneven surface having a large refractive index difference at the interface) other than the interface between the substrate and the recording layer, it greatly depends on the refractive index of the recording layer. Without using the substrate deformation recording method of the present invention, a high degree of modulation can be obtained. In the present invention,
It is not necessarily required to make the thickness of the recording layer approximately equal to the groove portion and the groove portion of the pre-groove. That is, if the refractive index of the recording layer can be sufficiently ensured with respect to the recording / reproducing wavelength, the groove portions and the inter-groove portions of the pre-groove and the thickness of the recording layer may be arbitrarily set.

In the recording mode of the present invention, the width of the groove bottom and the width of the groove opening of the substrate are mainly increased by substantially the same amount of increase. It may be accompanied by a change in the refractive index or expansion (bump) at the bottom of the substrate. In the present invention, the material of the recording layer is not limited to an organic material, and any material having an effect of absorbing a laser beam and expanding a groove width can be used. The action of widening the groove width can be obtained by the temperature rise of the recording layer material, gas generation, decomposition, explosion, expansion action and the like. Although the recording layer material itself does not cause any physical change from the beginning, an effect of generating a distortion in an adjacent layer by a rise in temperature and cooling by absorption of laser light may be used.

[0013]

The present invention will be described below in more detail with reference to examples. Example 1 As shown in FIG. 3A, the groove shape of the substrate in an unrecorded state is (A, B, C, D, ζ) = (0.10λ, 0.30).
.lambda., 0.40.lambda., 1.14.lambda., dg) (groove parameters are shown in FIG. 1).
(A, B, C, D, ζ) = (0.10) as shown in FIG.
λ, 0.60λ, 0.70λ, 1.14λ, dg), the modulation degree (where α = β = 0.30λ) is
The refractive index n and the substrate groove depth dg were calculated as parameters. The modulation degree is ((sum signal obtained from unrecorded portion)
− (Sum signal obtained from recorded portion) / (sum signal obtained from unrecorded portion). The recording layer was formed such that the interface between the recording layer (2) and the reflective layer (3) became flat as shown in FIG.

The details of the simulation conditions are as follows (the length is shown in units of the recording / reproducing wavelength λ). FIG. 5 shows the results. In FIG. 5, the recording / reproducing wavelength is assumed to be 650 nm, and the groove depth (Groove depth) is expressed in nm (nm display value = λ display value × 650 nm). From this result, it was found that a high degree of modulation was obtained when the groove depth was somewhat large and the refractive index of the recording layer was around 2.2 to 2.4, and the effect of the present invention was confirmed.

(Details of calculation conditions) Beam shape: Gaussian distribution Radius at which amplitude is 1 / e (x direction, y direction): 5000
λ, 5000λ Objective lens aperture radius: 3000λ Objective lens NA (numerical aperture): 0.60 Objective lens focal length: 5000λ Groove shape (A, B, C, D, ζ) (see FIG. 1): Before recording (0. 10λ, 0.30λ, 0.40λ, 1.1
4λ, dg) After recording (0.10λ, 0.60λ, 0.70λ, 1.1
4λ, dg) Refractive index of substrate: 1.58 (incident on substrate side) Refractive index of recording layer: ni−0.05 Film thickness d of recording layer (see FIGS. 3 and 4): 0.1λ Refractive index of reflective layer: 0.13 -I 3.16 Reflection layer thickness: 0.23λ Detector: 4-split PD Radius of detector (x direction, y direction): 3000λ, 300
0λ

Example 2 The modulation was calculated under the same calculation conditions as in Example 1 except that the film thickness of the recording layer (2) was made equal between the groove (groove) and the space between the grooves (land). (See FIG. 4). FIG. 6 shows the results. In FIG. 6, the recording / reproducing wavelength is assumed to be 650 nm, and the groove depth (Groove depth) is n.
m display (nm display value = λ display value × 650 nm).
From this result, it was found that a high degree of modulation was obtained when the groove depth had a certain characteristic, and the effect of the present invention was confirmed. Further, from the results shown in FIG. 6, it is possible to reduce the dependency of the degree of modulation on the refractive index of the recording layer (a phenomenon in which the degree of modulation varies greatly depending on the refractive index of the recording layer) with the optical recording medium of the present invention. It has been confirmed that it is possible to suppress a change in the recording / reproducing characteristics due to the wavelength fluctuation. Also,
With the optical recording medium of the present invention, it is possible to use a material other than a material having a very high refractive index as conventionally used as a recording layer material, for example, to eliminate the presence of a high refractive material in an organic material. Even in the short wavelength range,
It has been confirmed that a write-once optical recording medium can be easily realized.

[0017]

As described above, as is apparent from the detailed and specific description, the optical recording medium and the recording method of the present invention provide:
It is possible to provide a write-once optical recording medium with which a high degree of modulation can be easily obtained. Further, according to the optical recording medium and the recording method of the present invention, the refractive index dependence (wavelength dependence) of the recording layer.
Can be greatly improved. Further, for example, 4
Even in a short wavelength region of around 00 nm, a write-once optical recording medium having a recording layer made of an organic material can be easily realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a substrate groove shape in an unrecorded state of an optical recording medium of the present invention.

FIG. 2 is a diagram showing an unrecorded state and a substrate groove shape after recording of the optical recording medium of the present invention.

FIG. 3 is a diagram showing the unrecorded state and the shape of an optical recording medium after recording in Example 1 of the present invention.

FIG. 4 is a diagram showing an unrecorded state and a shape of an optical recording medium after recording in Example 2 of the present invention.

FIG. 5 is a diagram illustrating a modulation degree according to the first embodiment.

FIG. 6 is a diagram illustrating a modulation degree according to the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 recording layer 3 reflective layer 溝 substrate groove depth A substrate groove droop amount CB substrate groove droop amount BA width of substrate groove bottom C width of substrate groove top (groove opening width) D track pitch

Claims (9)

[Claims] 1. An optical recording medium having a recording layer provided on a substrate having at least a pre-groove, wherein a recording portion formed in a groove of the pre-groove has a groove bottom width of the substrate by irradiation of a laser beam. The optical recording medium is formed by enlarging the groove opening width by substantially the same increment. 2. An optical recording medium in which a recording layer and a reflection layer are sequentially provided on at least a substrate having a pre-groove, wherein a recording portion formed in a groove of the pre-groove is formed by irradiating the substrate with laser light. An optical recording medium formed by enlarging the groove bottom width and the groove opening width by substantially the same increment. 3. An optical recording medium in which a recording layer made of an organic material is provided on at least a substrate having a pre-groove, wherein a recording portion formed in a groove of the pre-groove is used for recording by laser light irradiation. An optical recording medium formed by enlarging a groove bottom width and a groove opening width of a substrate by substantially the same increment by a rise in temperature of a layer material. 4. An optical recording medium in which a recording layer made of an organic material and a reflection layer are sequentially provided on at least a substrate having a pre-groove, wherein a recording portion formed in a groove of the pre-groove is a laser beam. An optical recording medium formed by enlarging the groove bottom width and groove opening width of the substrate by substantially the same amount of increase by the temperature rise of the recording layer material due to the irradiation. 5. The light according to claim 1, wherein the thickness of the recording layer formed on the pre-groove is substantially equal in the groove and in the space between the grooves. recoding media. 6. A method for recording on an optical recording medium having a recording layer provided on at least a substrate having a pre-groove and having a recording portion formed in a groove of the pre-groove, wherein the substrate is irradiated with laser light. Forming the recording portion by enlarging the width of the groove bottom and the width of the groove opening by substantially the same amount of increase. 7. A method for recording on an optical recording medium having a recording portion in which a recording layer and a reflection layer are sequentially provided on at least a substrate having a pre-groove, and wherein the recording portion is formed in a groove of the pre-groove. The recording portion is formed by enlarging the groove bottom width and the groove opening width of the substrate by substantially the same amount of increase by irradiating the recording medium. 8. A method for recording on an optical recording medium comprising a recording layer made of an organic material provided at least on a substrate having a pre-groove and having a recording portion formed in a groove of the pre-groove, comprising: The recording portion is formed by enlarging the groove bottom width and the groove opening width of the substrate by substantially the same amount of increase by increasing the temperature of the recording layer material due to the irradiation of the optical recording medium. 9. A method for recording on an optical recording medium having a recording layer formed of an organic material and a reflective layer sequentially formed on at least a substrate having a pre-groove and having a recording portion formed in a groove of the pre-groove. Recording the optical recording medium by enlarging the groove bottom width and the groove opening width of the substrate by substantially the same amount of increase by increasing the temperature of the recording layer material due to laser light irradiation. Method.