JP2002324319A - Optical recording medium and its recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply obtain a high recorded contrast (modulation) for an optical recording medium that has a recording layer on a plate having a pre-groove at least, and provide its recording method. SOLUTION: (1) This optical recording medium has a recording layer on a plate having a pre-groove at least, and forms a recorded section changing in width of the pre-groove by irradiating a laser beam, and is characterized in that the recorded section is formed by enlarging the opening width of the groove against the width at the groove bottom on the plate. (2) This recording method is a recording method on an optical recording medium having a recording layer on a plate having a pre-groove at least, and forms a recorded section changing in width of the pre-groove by irradiating a laser beam, and featured in that the recorded section is formed by enlarging the opening width of the groove against the width at the groove bottom on the plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical recording medium and a recording method thereof.

[0002]

2. Description of the Related Art Conventionally, optical recording media having an organic material as a recording layer, such as CD-R and DVD-R, have been put to practical use. In these optical recording media, for example, “SPIE Vol. 107
8 Optical Data Storage To
pical Meeting (1989) pp. 80-
87 "and" Jpn. J. Appl. Phys. Vol.
31 (1992) pp. 484-493 "describes that 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. Also, "J
pn. J. Appl. Phys. Vol. 36 (199
7) pp. 403-409 "includes the CNR of the reproduced signal.
(Carrier to noise ratio, carrier to noise
Noise ratio) is described as having a correlation with the expansion height and expansion width of the substrate bottom due to recording. Furthermore,
http: // search. zdnet. co. jp
/ Magazine / cshop / 0012 / sp3
(Computer Shopper Japan H
home page), as a recording principle of CD-R,
There is a description that the reflectance of light is reduced due to the deterioration of the dye and the material of the substrate. orangef
orum. or. jp / j / cdr / cdr mech
anisml. htm (CDs conforming to the Orange Book
-The official site of the Orange Forum, a corporate organization for disseminating the R / RW standard, states that the recording principle of CD-R is that recording pits are formed due to refractive index changes due to substrate deformation and dye decomposition. There is a description.

On the other hand, as a recording method of an optical recording medium,
"Optical disc technology, supervised by Morio Onoe, Radio Engineering, 31
As described in "page 5", recording methods such as a punching type, a phase change type, a bubble type, and a texture type have been proposed as recording methods for a write-once optical disc. Patent No. 2710
No. 040 discloses a recording method for obtaining a high degree of modulation in a CD-R optical disc, in which a bump (expanded portion) is formed on a substrate, a deteriorated portion of optical characteristics is formed on a recording layer, or a recording layer is formed. 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 having optical characteristics is formed on the substrate. JP-A-8-7275 discloses that a laser beam is applied to an optical recording medium having a recording layer made of a shape memory resin provided directly or via a dielectric layer on a transparent substrate in the vicinity of the interface of the recording layer on the substrate side. There has been proposed a recording method in which a convex pit is formed by irradiating the shape memory resin so as to be focused and thermally expanding the shape memory resin.

[0004]

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. For example, “Jpn.J. Appl.P
hys. Vol. 31 (1992) pp. 484-49
As described in 3), in order to secure a high degree of modulation and a high reflectance, the refractive index of the recording layer material needs to be 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 caused to lower the reflectance. Therefore, there are the following problems (a) to (e). I. A very large load is applied to the selection of the recording layer material. B. The cost does not decrease when the optical properties can be satisfied only by a material that requires time for synthesis. C. Since a region having a large refractive index is used, there is a very large wavelength dependency. D. It is difficult to develop a write-once optical recording medium having a recording layer made of an organic material in a wavelength region where it is difficult to increase the refractive index, for example, a wavelength region of 450 nm or less (the molecular extinction coefficient decreases as the absorption wavelength decreases). Therefore, it is very difficult to achieve a high refractive index in a short wavelength region). E. In addition to optical characteristics, good thermal decomposition characteristics (characteristics of decomposing at low temperature in a short time) are required.

[0005] A write-once optical recording medium using an inorganic material also requires a recording method capable of obtaining good recording characteristics. Accordingly, 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 pre-groove and capable of easily obtaining a recording contrast (modulation degree), and a recording method thereof. It is another object of the present invention to provide an optical recording medium which solves the problem of large wavelength dependence of recording characteristics, which is peculiar to a write-once optical recording medium having a recording layer made of an organic material, and a recording method thereof. Further, even when the recording / reproducing wavelength is shortened, for example, even when the wavelength is around 400 nm, an optical recording medium capable of easily realizing a write-once optical recording medium having a recording layer made of an organic material, and the like. The purpose is to provide a recording method.

[0006]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that an optical recording medium in which a recording layer is provided on at least a substrate having a pre-groove and a recording portion is formed in a groove of the pre-groove, In a recording method (recording principle) conventionally proposed such as expansion of a substrate (bump), decomposition of a recording layer material, deformation of a reflective layer, etc., a sufficient recording contrast (modulation degree) depends on a refractive index of the recording layer material. In order to improve the problem that the recording layer cannot be obtained, the present inventors have newly found a recording method capable of obtaining a sufficient recording contrast (modulation degree) without largely depending on the refractive index of the recording layer material.
In the recording method (recording principle) of a conventional write-once optical recording medium having a recording layer made of an organic material, there were very severe restrictions on the physical property values of the recording layer material. It has been found that the method can alleviate the strict physical property value restrictions imposed on the recording layer material.

[0007] That is, the above problems are solved by the following inventions 1) to 9). 1) An optical recording medium in which a recording layer is provided on at least a substrate having a pre-groove, and a recording portion is formed in a groove of the pre-groove as a change in groove width by irradiation with laser light, wherein a width of a groove bottom of the substrate is provided. An optical recording medium, characterized in that a recording portion is formed by making the groove opening width increase amount larger than the increase amount. 2) An optical recording medium in which a recording layer is provided on at least a substrate having a pre-groove, and a recording portion is formed as a change in groove width in a groove of the pre-groove by irradiation of a laser beam, the width of a groove bottom of the substrate being An optical recording medium characterized in that a recording portion is formed by enlarging only a groove opening width of a substrate without changing the recording medium. 3) The optical recording medium according to 1) or 2), wherein a reflective layer is further provided on the recording layer. 4) The optical recording medium according to any one of 1) to 3), wherein the recording layer is made of an organic material. 5) The optical recording medium according to any one of 1) to 4), 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. 6) A recording method for an optical recording medium in which a recording layer is provided on a substrate having at least a pre-groove, and a recording portion is formed as a change in groove width in a groove of the pre-groove by irradiation of a laser beam. A recording portion formed by increasing the groove opening width increase amount with respect to the groove bottom width increase amount. 7) A method for recording on an optical recording medium in which a recording layer is provided on at least a substrate having a pre-groove and a recording portion is formed as a change in groove width in a groove of the pre-groove by irradiating a laser beam. Without changing the groove bottom width of
A recording method wherein a recording portion is formed by enlarging only a groove opening width of a substrate. 8) The recording method according to 6) or 7), wherein the optical recording medium has a reflective layer further provided on a recording layer. 9) The recording method according to any one of 6) to 8), wherein the recording layer of the optical recording medium is made of an organic material.

Hereinafter, the present invention will be described in detail. The groove shape of the substrate in the unrecorded state of the optical recording medium having the pre-groove is, for example, as shown in FIG.
ζ, substrate groove dripping amounts: A and CB, substrate groove bottom width: BA, substrate groove top width (groove opening width): C, track pitch: D (land) A, B, C, and D are set starting from the edge of the section). In the present invention, as shown in FIG. 2A, the groove shape in the unrecorded state [width of groove bottom: (B-A), width of groove above groove (groove opening width): C] (see FIG. 2 only shows the substrate), and as shown in FIG. 2B, the width of the groove bottom of the substrate is (BA) + α by recording and the width of the upper part of the substrate groove (groove opening width) is C + β. A recording method for enlarging, where β>α>
0, or β> 0 and α ≒ 0.
With this recording method, it is possible to easily obtain a high degree of modulation.

In the present invention, it is preferable to use this recording method to make the thickness of the recording layer substantially equal between the groove portion and the inter-groove portion of the pre-groove, whereby the dependence of the degree of modulation on the refractive index of the recording layer is greatly reduced. Can be 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 and 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 reflective layer.

Since 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, the refractive index of the recording layer is reduced and the difference in refractive index between the substrate and the substrate is small. Then, even if the change in the optical characteristics of the recording layer material or the change in the substrate groove shape 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 the 0th-order light and ± 1st-order light is used for tracking, but the refractive index of the recording layer decreases. When the difference in the refractive index from the substrate is reduced, the diffraction effect is mainly caused by the unevenness at 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 ’s happening,
The degree of modulation is reduced.

Therefore, in a preferred embodiment of the present invention, the above-mentioned recording method 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. Further, the groove portions and the inter-groove portions of the pre-groove and the recording layer film thickness were made substantially equal. This recording method positively utilizes that the substrate or the recording layer and the air layer or the reflection layer have a large refractive index difference even if the recording / reproducing wavelength is shortened. That is, by setting beforehand an interface having a large refractive index difference that causes a phase change (unevenness having a large refractive index difference at the interface) other than the interface between the substrate and the recording layer, the refractive index of the recording layer becomes large. A high degree of modulation can be obtained by the substrate deformation recording method of the present invention without dependence.

In the present invention, it is not always necessary to make the thickness of the recording layer substantially equal to that of the groove portion between the pregrooves and the groove portion. The groove portions and the inter-groove portions of the groove and the thickness of the recording layer may be arbitrary. The recording method of the present invention is mainly intended to make the groove opening width increase amount larger than the groove bottom width increase amount of the substrate. However, as the substrate groove width increases, the refractive index of the recording layer material changes and the substrate bottom width increases. May be accompanied by expansion (bump). Further, in the present invention, an organic material is preferably used as a recording layer material, but is not limited thereto, and any material having an effect of absorbing a laser beam and expanding a groove width may be used. Can be. 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 increasing the temperature and cooling by absorption of the laser beam may be used.

[0013]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Embodiment 1 As shown in FIG. 3A, the groove shape of the substrate in the unrecorded state is (A,
B, C, D, ζ) = (0.10λ, 0.30λ, 0.4
0λ, 1.14λ, 0.25λ) (see FIG. 1 for the definition of the groove parameter).
(A, B, C, D, ζ) = [aλ, (a)
+0.2) λ, (2a + 0.2) λ, 1.14λ, 0.
25λ], where a = 度 (C
+ Β)-[(B−A) + α]｝ / 2, β> 0 and α = 0], by changing the refractive index n of the recording layer and the amount of enlargement of the substrate groove opening [= (recorded groove (Opening width) − (groove opening width at the time of non-recording) = δ groove opening width (δGroove top widget)
h)] as a parameter. The degree of modulation is
[(Sum signal obtained from unrecorded portion)-(sum signal obtained from unrecorded portion)] / (sum signal obtained from unrecorded portion)]. The recording layer was formed such that the interface between the recording layer and the reflective layer was flat, as shown in FIG. The details of the simulation conditions are as described below (the length is shown in units of the recording / reproducing wavelength λ), and the result is as shown in FIG. In FIG. 5, the recording / reproducing wavelength is 650 (n).
m) and the amount of expansion of the substrate groove opening [δ groove opening width (δ
[Groove top width]] was expressed in nm [nm display value = λ display value × 650 (nm)]. From this result, it was found that a high degree of modulation could be obtained when the recording layer had a refractive index of 2.3 or more with a specific groove opening width expansion amount, and the effect of the present invention was confirmed.

(Details of simulation conditions) Beam shape: Gaussian distribution Radius where amplitude is 1 / e (x direction, y direction): 500
0λ, 5000λ ・ Object 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): recording Before (0.10λ, 0.30λ, 0.40λ, 1.14λ,
0.25λ) After recording [aλ, (a + 0.2) λ, (2a + 0.2)
[lambda], 1.14 [lambda], 0.25 [lambda]]-substrate refractive index: 1.58 (substrate side incidence)-recording layer refractive index: ni-0.05-recording layer thickness d (see Figs. 3 and 4): 0. 1 λ ・ Refractive index of reflective layer: 0.13-i3.16 ・ Thickness of reflective layer: 0.23λ ・ Detector: 4-split PD ・ Radius of detector (x direction, y direction): 3000λ, 30
00λ

Example 2 In Example 1, except that the film thickness of the recording layer was made equal between the groove portion (groove) and the inter-groove portion (land) (see FIG. 4).
The degree of modulation was calculated under the same conditions as in Example 1. The result is as shown in FIG. In FIG. 6, the recording / reproducing wavelength is 6
Assuming 50 (nm), the amount of enlargement of the opening of the substrate groove [δ Groove top width] is nm
[Nm display value = λ display value × 650 (n
m)]. From this result, it was found that as the groove opening width was increased, a very high degree of modulation was obtained, and the effect of the present invention was confirmed. Further, from the results shown in FIG. 6, according to the optical recording medium of the present invention, it is possible to reduce the dependency of the modulation degree on the refractive index of the recording layer (a phenomenon in which the modulation degree is largely changed by the refractive index of the recording layer). It has been confirmed that it is possible to suppress the change in the recording / reproducing characteristics caused by the wavelength fluctuation of. Further, the optical recording medium of the present invention enables to use a material other than a material having a very high refractive index as conventionally used as a recording layer material, for example, a high refractive material of an organic material exists. It has been confirmed that a write-once optical recording medium can be easily realized even in such a short wavelength range that disappears.

[0017]

According to the optical recording medium and the recording method of the present invention, it is possible to provide a write-once optical recording medium capable of easily obtaining a high degree of modulation and a recording method thereof. Further, according to the optical recording medium and the recording method of the present invention, it is possible to greatly improve the refractive index dependence (wavelength dependence) of the recording layer. Further, even in a short wavelength region of, for example, around 400 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 view showing a substrate groove shape in an unrecorded state of an optical recording medium having a pregroove.

FIG. 2A is a cross-sectional view showing a groove shape of a substrate in an unrecorded state. (B) Sectional view showing the groove shape of the substrate after recording.

FIG. 3A is a sectional view of an optical recording medium according to a first embodiment in an unrecorded state. (B) Sectional view of the optical recording medium of Example 1 after recording.

FIG. 4A is a cross-sectional view of an optical recording medium according to a second embodiment in an unrecorded state. (B) A sectional view of the optical recording medium of Example 2 after recording.

FIG. 5 is a diagram showing a result of calculating a modulation degree of the optical recording medium of Example 1 using a refractive index n of a recording layer and an enlargement amount of a substrate groove opening as parameters.

FIG. 6 is a view showing a result of calculating a modulation degree of the optical recording medium of Example 2 using a refractive index n of a recording layer and an enlargement amount of a groove opening of a substrate as parameters.

[Explanation of symbols]

 A: Groove amount of substrate groove CB: Groove amount of substrate groove BA: Width of groove bottom of substrate C Width of groove top of substrate (groove opening width) D Track pitch 溝 groove depth of substrate

Claims (9)

[Claims] An optical recording medium comprising: a recording layer provided on a substrate having at least a pre-groove; and a recording portion formed as a change in groove width in a groove of the pre-groove by irradiation of a laser beam. An optical recording medium characterized in that a recording portion is formed by increasing the groove opening width increase amount with respect to the groove bottom width increase amount. 2. An optical recording medium comprising: a recording layer provided on a substrate having at least a pre-groove; and a recording portion formed as a change in groove width in a groove of the pre-groove by irradiation of a laser beam. An optical recording medium, wherein a recording portion is formed by enlarging only a groove opening width of a substrate without changing a groove bottom width. 3. The optical recording medium according to claim 1, wherein a reflection layer is further provided on the recording layer. 4. The optical recording medium according to claim 1, wherein said recording layer is made of an organic material. 5. The optical recording 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. Medium. 6. A method for recording on an optical recording medium wherein a recording layer is provided on at least a substrate having a pre-groove, and a recording portion is formed as a change in groove width in a groove of the pre-groove by irradiation of a laser beam. And forming the recording portion by increasing the groove opening width increase amount with respect to the groove bottom width increase amount of the substrate. 7. A method for recording on an optical recording medium wherein a recording layer is provided on at least a substrate having a pre-groove, and a recording portion is formed as a change in groove width in a groove of the pre-groove by irradiation of laser light. A recording portion formed by enlarging only the groove opening width of the substrate without changing the groove bottom width of the substrate. 8. The optical recording medium according to claim 6, wherein a reflection layer is further provided on the recording layer.
Or the recording method according to 7. 9. The recording method according to claim 6, wherein the recording layer of the optical recording medium is made of an organic material.