JP2008034011A - Optical information recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording medium capable of reducing cross erasure of an adjacent track, recording signals in a narrow track and performing high density recording and reproduction combined with a mask effect (reduction of cross talk) during reproduction. <P>SOLUTION: In the optical information recording medium having a substrate 20 wherein track grooves 22 are formed by providing recessed parts 20A and projecting parts 20B on the surface thereof, a recording layer 28 recording information by using laser light L and a mask layer 32 wherein an optical mask part is formed in an optical spot by change of light transmittance according to radiation intensity of the laser light, the recording layer is provided corresponding to only either one of the recessed parts and the projecting parts. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical information recording medium that records and reproduces information by irradiating a laser beam, and a manufacturing method thereof.

In general, optical discs such as CDs (Compact Discs) and DVDs (Digital Versatile Discs) are known as optical information recording media for recording and reproducing information by laser light.
Various optical recording systems for this optical disc are known. For example, the phase change type optical recording system is crystallized by using a phase change recording medium or the like to locally raise the temperature by laser irradiation. The basic principle is to change the optical characteristics such as the refractive index of the material by changing the material to an amorphous state, and to detect the change in the amount of reflected laser light. In order to improve the recording density, it is necessary to shorten the recording bit length, that is, to miniaturize the information mark.

  However, the signal reproduction resolution is almost determined by the wavelength λ of the light source and the numerical aperture NA of the objective lens in the optical pickup of the reproduction optical system, and the spatial frequency 2NA / λ is the reproduction limit. Therefore, it is conceivable to shorten the wavelength λ of the light source in order to increase the recording density, or to reduce the diameter of the light spot of the reproducing apparatus using a high NA lens. However, in the Blu-ray Disc currently in practical use, the laser beam wavelength is set to about 405 nm and the numerical aperture NA of the lens is set to 0.85. The limit of improvement in recording density due to the numerical aperture NA of the objective lens has been reached.

  An example of a reproduction method that solves the problem of the limit of recording density that depends on the reproduction resolution of the optical pickup is disclosed in Patent Document 1. This reproducing method is an optical recording medium in which a recording layer for reproducing or recording / reproducing using a laser beam and an auxiliary layer whose light transmittance changes according to the intensity of irradiated light are laminated. , A light transmittance changing material whose light transmittance changes temporarily according to the intensity of irradiated light, thereby reducing the effective light spot size to a small size, thereby improving the reproduction resolution It is.

  Here, the structure of a conventional optical disc will be described with reference to FIG. As shown in FIG. 6, this optical disc D has a light-transmitting substrate 2 having concave and convex portions (not shown) on the surface. A mask layer 4 is provided on the surface of the substrate 2 (the lower surface in the drawing). This mask layer is made of a light transmittance changing material whose light transmittance is temporarily changed according to the intensity of the irradiated laser beam, thereby reducing the effective light spot size. A first dielectric layer 6, a recording layer 8, a second dielectric layer 10 and a protective layer 12 are sequentially laminated on the mask layer 4. The recording layer 8 is made of a phase change material.

  In the optical disk D configured as described above, when the light spot of the laser beam L to be reproduced or recorded / reproduced is incident on the mask layer 4, the light transmission of the mask layer 4 is performed in the central portion where the light intensity of the light spot showing the Gaussian distribution is strong. The light transmittance of the mask layer 4 decreases in the peripheral portion where the light intensity is weak in the light spot. As a result, the diameter of the light spot is substantially reduced, and the recording / reproducing resolution is improved. Attempts have been made to improve the recording density by combining the mask layer 4 made of the light transmittance changing material and the recording layer 8 made of the phase change recording material.

Japanese Patent Laid-Open No. 5-28535

However, in order to more efficiently increase the density, the mask effect at the time of reproduction as disclosed in Patent Document 1 is not always sufficient. This is because in high-density recording with an increased track density, it is difficult to reduce the cross erase of adjacent tracks without reducing the size of the recording mark by thermal recording.
The present invention has been devised to pay attention to the above problems and to effectively solve them. The object of the present invention is to reduce cross erase of adjacent tracks, record signals on extremely thin tracks, and enable high-density recording / reproduction in combination with the mask effect (reduction of crosstalk) during reproduction. An optical information recording medium and a manufacturing method thereof are provided.

  According to the first aspect of the present invention, there is provided a substrate in which a track groove is formed by providing a concave portion and a convex portion on the surface, a recording layer for recording information by laser light, and light transmittance according to the irradiation intensity of the laser light. And an optical information recording medium having a mask layer in which an optical mask portion is formed in the light spot by changing the recording layer on only one of the concave portion and the convex portion. An optical information recording medium is characterized in that it is provided so as to correspond thereto.

  According to the second aspect of the present invention, there is provided a substrate in which track grooves are formed by providing concave and convex portions on the surface, a recording layer for recording information by laser light, and light transmittance according to the irradiation intensity of the laser light. And a mask layer in which an optical mask portion is formed in a light spot by changing, and a thin film for the recording layer is formed on the entire surface on the substrate side. And a step of forming the recording layer by selectively removing the thin film for the recording layer corresponding to the concave portion or the convex portion. Is the method.

  According to the optical information recording medium and the method of manufacturing the same according to the present invention, it is possible to reduce the cross erase of adjacent tracks, record a signal on an extremely thin track, and to reduce the mask effect during reproduction (crosstalk reduction). Together, high-density recording / reproduction can be performed.

In the following, an embodiment of the optical information recording medium and the manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a partially enlarged cross-sectional view showing an example of an optical information recording medium according to the present invention. FIG. 2 is a schematic diagram showing the intensity distribution of light incident on a mask layer and the intensity distribution of light transmitted through the mask layer. 3 is a diagram showing the relationship between the intensity of light incident on the mask layer and the transmittance, and FIG. 4 is a process diagram showing the main part of the method for producing an optical information recording medium according to the present invention.

As shown in FIG. 1, an optical disk D1 as an example of the optical information recording medium has a thin disk-shaped substrate 20. A track groove 22 is formed on the surface of the substrate 20 (upper surface in the drawing) by alternately providing concave portions 20A and convex portions 20B. The track grooves 22 are formed concentrically or spirally.
On the surface on which the track groove 22 is formed, the reflective layer 24, the second dielectric layer 26, the recording layer 28, the first dielectric layer 30, the mask layer 32, and the protective layer 34, which are features of the present invention. Are sequentially formed. Here, the laser beam L is incident from the protective layer 34 side, and forms a light spot SP therein.

  Here, the recording layer 28 is not formed on the entire surface on the substrate 20 side, but is provided along only one of the concave portion 20A and the convex portion 20B. Therefore, in the sectional view, the recording layer 28 is divided at a predetermined pitch. In FIG. 1, it is provided corresponding to the recess 20. Accordingly, the recess 20 becomes a recording track, and this width becomes the track width W. The distance between adjacent recording tracks is the track pitch P.

In this case, since the laser beam L is incident from the opposite side, the substrate 20 may or may not be light transmissive. For example, a glass plate or a polycarbonate substrate can be used. When laser light is incident from the substrate 20 side, a light transmissive material is used.
As the reflective layer 24, for example, an aluminum alloy or the like can be used. The reflective layer 24 is laminated by sputtering in a vacuum.

Then, the second dielectric layer 26 is formed on the reflective layer 24 by, for example, sputtering. The second dielectric layer 26 is made of, for example, ZnS + SiO ₂ or SiNx (silicon nitride film).
A recording layer 28 is formed on the second dielectric layer 26 at a portion corresponding to the recess 20A. The recording layer 28 is a so-called phase change recording thin film capable of phase transition between crystal and amorphous depending on the irradiation intensity of laser light. A method for forming the recording layer 28 will be described later.

A first dielectric layer 30 is formed by sputtering, for example, on the second dielectric layer 26 so as to cover the recording layer 28. The first dielectric layer 30 is a transparent film that becomes a protective film or a multiple interference film. The first dielectric layer 30 is made of, for example, ZnS + SiO ₂ or SiNx (silicon nitride film).
Then, a mask layer 32 composed of one layer or two layers is formed on the first dielectric layer 30 by, for example, sputtering. Further, a protective layer 34 is formed on the mask layer 32. As the protective layer 34, for example, a UV (ultraviolet) curable resin, a thermosetting resin, or the like can be used.

  This optical disc D1 has a reverse stacking order compared to the optical disc D shown in FIG. 6, and in order to optically reduce the spot diameter of the reproduction laser beam, the reproduction objective with a high NA of about 0.85 is used. In the case of using a lens, it is necessary to thin the protective layer 34 through which light passes, and such a configuration is desirable.

  In the optical disc D1 configured as described above, when the light spot SP to be reproduced or recorded / reproduced enters the mask layer 32, the light transmittance of the mask layer 32 increases in the central portion where the light intensity is strong among the light spots SP. Of the light spot SP, the light transmittance of the mask layer 32 decreases in the peripheral portion where the light intensity is weak. As a result, the central portion where the light intensity is high in the light spot SP is higher in intensity than the peripheral portion, and the peripheral portion where the light intensity is low in the light spot SP is higher than that in the central portion. Strength decreases. That is, the diameter of the light spot SP is substantially reduced and is incident on the recording layer 28.

  The recording layer 28 is a recording layer that is reproduced or recorded / reproduced using a light spot having a light intensity distribution (for example, Gaussian distribution) as shown in FIG. The information on the optical disk is read by the reflected light or transmitted light. The mask layer 32 is made of a light transmittance changing material whose light transmittance temporarily changes depending on the intensity of irradiated light, for example, a cyclic organometallic complex, a phase change material, a photochromic, etc., and is incident as shown in FIG. The greater the intensity of the light, the greater the light transmittance.

  When the reproduction laser beam is irradiated with the light spot, the mask layer 32, which is a light transmittance changing material, has optical characteristics of light intensity and light transmittance as shown in FIG. The spot SP diameter is substantially reduced. That is, when the spot light X (light spot diameter x) having the light intensity distribution shown in FIG. 2 is incident on the mask layer 32 which is a light transmittance changing material, the central portion having a high intensity is compared with the peripheral portion having a low intensity. Since the light transmittance is high, more light is transmitted and transmitted. In the peripheral portion where the intensity is low, the light transmittance is small compared to the central portion where the intensity is high. As shown in FIG. 4, the light beam enters the recording layer 28 as a sharp light spot Y (substantial light spot diameter y) having a small light spot diameter. As a result, high-density reproduction is possible with the light spot Y having a small diameter y.

  Here, the degree of reduction of the light spot diameter will be described. For ease of explanation, assuming that the light transmittance characteristic as indicated by the dotted line in FIG. 3 in which the intensity of the incident light and the light transmittance are approximately proportional, the light spot diameter is reduced to about 3/4. Actually, since it has the characteristic as shown by the solid line in FIG. 3, the light spot diameter is further reduced to substantially 3/5. When the reflected light is detected, it passes through the mask layer 32, which is a change in light transmittance, twice, so the light spot diameter is further reduced to 1/2 to 1/3, and the recording density is about 4 times to 9 times. Double.

  As described above, the mask layer 32 is a light transmittance changing material whose light transmittance changes (temporarily) depending on the intensity of irradiated light, for example, a cyclic organometallic complex, a phase change material, a photochromic, and the like. As shown in FIG. 2, the light transmittance increases as the intensity of incident light increases. As this light transmittance changing material, a zirconium porphyrin complex which is a cyclic organometallic complex having two alkyl groups can be used. When the zirconium porphyrin complex is irradiated with a light spot for reading (wavelength> 400 nm), a zirconium porphyrin complex having no alkyl group is formed, and the light transmittance changes temporarily depending on the light intensity distribution of the light spot. To do. As a result, as described above, the substantial diameter of the light spot is reduced. When the light spot for reading is no longer irradiated, it is restored by recombination.

  Further, a phase change material may be used as the light transmittance changing material. As the phase change material, for example, many materials such as Te—Ge—Sb, Te—Sn—Se, Te—Ga—Se, and In—Sb are known. The phase change material is usually in a crystalline state (heating or light irradiation) and in a state of poor light transmittance. When it is heated to a molten state with reproduction light, it becomes amorphous and the transmittance temporarily changes. As a result, as described above, the substantial diameter of the light spot is reduced. When the reading light spot is no longer irradiated, the phase change material is cooled and returned to the crystalline state again. Transmittance deteriorates. These phase change materials can be formed by sputtering or vapor deposition, and can be formed continuously or in the same vacuum layer as the reflective layer 24, so that productivity is good. In addition, the wavelength dependency of light is small, it is sensitive to any light in the ultraviolet to infrared wavelength range, and can change over a wide range.

Next, a method for forming the recording layer 28, which is a feature of the present invention, will be described with reference to FIG.
In FIG. 4A, the reflective layer 24 and the second dielectric layer 26 are sequentially formed on the substrate 20 by a normal method, and the recording layer 28 is formed on the entire surface of the uppermost layer. The state in which the thin film 40 for layers has already been formed is shown.

  Then, in the state shown in FIG. 4A, for example, by performing an ion milling process, the ion beam 42 is blown off, and the thin film 40 other than the portion corresponding to the recess 20A is scraped off. As shown, the separated recording layer 28 is formed. In this ion milling step, for example, krypton ions can be used. This ion milling process can be performed in the middle of a thin film forming process of continuously forming a film in a vacuum, and does not disturb other film forming orders. The incident direction of the ion beam used for ion milling is not necessarily perpendicular to the film surface. Further, means such as reactive ion etching may be used as long as the desired thin film can be removed. After the ion milling step, the first dielectric layer 30, the mask layer 32, and the protective layer 34 are sequentially formed by a normal method to complete the optical disc D1.

  In order to reduce the cross erase to the adjacent track, it is necessary to prevent the recording heat due to the laser beam during recording from diffusing to the periphery. As described above, the recording layer 28 is arranged in the disk radial direction. By dividing into a narrow width, it is possible to prevent thermal diffusion. In other words, the recording layer 28 is divided in the radial direction of the disc to form a very narrow recording layer 28 extending in the circumferential direction of the disc, so that a minute mark is formed in an extremely narrow recording track, In addition, even when recording is performed on the adjacent track, the recording heat does not diffuse to the adjacent track in the disk radial direction, so that it is possible to prevent the recording mark from being deteriorated by cross erase.

  Next, the standardized jitter (jitter) was evaluated for the optical disc according to the present invention and the conventional optical disc configured as described above, and the evaluation results will be described. FIG. 5 is a diagram showing the relationship between the normalized jitter and the reproduction mark length of the optical disc of the present invention and the conventional optical disc.

  Here, the track pitch is set to 320 nm for the conventional optical disc without the mask layer, and the track pitch is set to 160 nm, which is half as narrow as the conventional disc, for the optical disc of the present invention having the mask layer, and the reproduction mark length is changed. The reproduction characteristics were measured respectively. Both discs compare the reproduction characteristics after recording signals on both sides of the reproduction track. In the conventional disk, when the reproduction mark length is 150 and 100 nm, the standardized jitter is 5.8 and 18.9%, respectively, and when the reproduction mark length becomes shorter than that, the detection becomes impossible.

  On the other hand, in the present invention, when the reproduction mark length is changed from 150 to 70 nm, the standard jitter is changed from 5.7 to 8.8%. We were able to confirm that it can be replayed. As a result, according to the disk of the present invention, a synergistic effect of the crosstalk reducing action by the mask layer 32 and the cross erasing reducing action by the recording layer 28 separated for each track in the disk radial direction is realized, and high reproduction performance is achieved. It can be seen that

As described above, according to the present invention, cross erase of adjacent tracks can be reduced by a new method, and a signal can be recorded on an extremely thin track, which is combined with a mask effect during reproduction (crosstalk reduction). Thus, an optical information recording medium capable of high-density recording / reproduction can be provided.
In the above embodiment, the recording layer 28 is provided corresponding to the concave portion 20A of the substrate 20, but instead, the recording layer may be provided corresponding to the convex portion 20B.
In addition, the laminated structure of each layer here is merely an example, and is not limited thereto.

Furthermore, in the present embodiment, the optical disk of the type in which the laser beam is irradiated from the protective layer 34 side has been described, but the present invention is not limited to this, and the type of laser beam irradiation from the substrate side as in the conventional disk shown in FIG. The present invention can also be applied to other optical discs.
Although an optical disk has been described as an example of an optical information recording medium here, the present invention can of course be applied to other recording media such as an optical information recording medium such as an optical information card.

It is a partial expanded sectional view which shows an example of the optical information recording medium based on this invention. It is the schematic diagram which showed intensity distribution of the light which injected into the mask layer, and intensity distribution of the light which permeate | transmits a mask layer. It is the figure which showed the relationship between the intensity | strength of the incident light to a mask layer, and the transmittance | permeability. It is process drawing which shows the principal part of the manufacturing method of the optical information recording medium based on this invention. It is a figure which shows the relationship between the standardized jitter and reproduction | regeneration mark length of the optical disk of this invention, and the conventional optical disk. It is a block diagram which shows the structure of the conventional optical disk.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Substrate, 20A ... Concave part, 20B ... Convex part, 22 ... Track groove, 24 ... Reflective layer, 26 ... Second dielectric layer, 28 ... Recording layer, 30 ... First dielectric layer, 32 ... Mask layer, 34 ... protective layer, 40 ... thin film for recording layer, D1 ... optical disc (optical information recording medium), L ... laser beam.

Claims (2)

A substrate in which track grooves are formed by providing concave and convex portions on the surface;
A recording layer for recording information by laser light;
In an optical information recording medium having a mask layer in which an optical mask portion is formed in a light spot by changing light transmittance according to the irradiation intensity of laser light,
An optical information recording medium, wherein the recording layer is provided so as to correspond to only one of the concave portion and the convex portion. A substrate in which track grooves are formed by providing concave and convex portions on the surface;
A recording layer for recording information by laser light;
In a method of manufacturing an optical information recording medium comprising: a mask layer in which an optical mask portion is formed in a light spot by changing light transmittance according to the irradiation intensity of laser light;
Forming a thin film for the recording layer on the entire surface on the substrate side;
Forming the recording layer by selectively removing the thin film for the recording layer corresponding to the concave portion or the convex portion; and
A method for producing an optical information recording medium, comprising:

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