JPH08297838A - Optical recording method - Google Patents

Abstract

PURPOSE: To obtain a recording method which is capable of forming good microrecording parts in order to realize high-density recording by utilizing phase differences, is capable of having a large recording modulation degree in spite of the slight rate of the change in the film thickness before and after recording and is adequate for short-wavelength recording of a wavelength of 620 to 690nm. CONSTITUTION: This optical recording method comprises making a laser beam of a wavelength of 620 to 690nm incident from a substrate side, changing the film thickness of a recording layer by 10 to 30% by the laser beam condensed onto guide grooves to induce the occurrence of the phase differences of the laser beam arriving at a reflection layer and reading the change in the reflected light quantity by the phase differences. The recording layer of the optical recording medium includes a resin having a glass transition point of >=50 deg.C and a main weight loss initiation temp. higher than 250 deg.C or a resin having the glass transition point of <50 deg.C and the main weight loss initiation temp. of 100 to 250 deg.C and org. dyestuff. The recording layer is otherwise the layer of the org. dyestuff alone having the main weight loss initiation temp. of 150 to 270 deg.C and the weight loss of 20 to 40% in a temp. region from the main weight loss initiation temp. to (the main weight loss initiation temp. +100 deg.C).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording method, and more particularly to an optical recording method capable of recording with laser light.

[0002]

2. Description of the Related Art In recent years, various optical discs using a laser beam as a light source have been developed, and particularly for high density recording, attention has been paid to shortening the oscillation wavelength of the laser beam, which is shorter than the current 780 nm and 830 nm. There is a demand for an optical recording medium capable of recording and reproducing with a laser beam having a short wavelength. Under such circumstances, various recording media have been proposed. Among them, an organic dye-based optical recording medium using an organic dye in a recording layer has a feature of being inexpensive and easy to manufacture in a process.

Among the organic dye-based optical recording media, a CD-compatible optical disc (CD-R) has already been put to practical use at 780 nm. On the other hand, examples of the organic dye-based medium for short wavelength use include, for example, JP-A-4-74690.
Japanese Patent Laid-Open No. 4-238036, Japanese Patent Laid-Open No. 5-3
A number of proposals have been made such as Japanese Patent No. 8878. These are the findings of CD-R at 780 nm applied for short wavelengths.

Regarding the use of the phase difference,
JP-A-57-501980 and JP-A-3-5474.
It is proposed in Japanese Patent Publication No. 4 and the like. However, the former is for recording on the mirror surface of the incident on the film surface, and the latter is not for the principle of recording that utilizes the phase difference itself, and is not mentioned even after recording. In addition to the above-mentioned JP-A-3-54744 and JP-A-54-500058, regarding the structure in which the polymeric material is a medium of a type including a light absorber and has a reflective layer, there is disclosed in JP-A-2- 504
Although proposed in Japanese Patent Publication No. 566, Japanese Patent Publication No. 6-12570, etc., it is difficult to form a recording portion that is sufficiently small for short wavelength applications.

[0005]

In the above-mentioned prior art, the recording modulation degree is obtained at the time of recording due to only the decomposition of the dye or both the decomposition of the dye and the deformation of the substrate. Since the deformation is large, in the case of recording on the groove, a large pit is formed extending to the space between adjacent grooves, which causes crosstalk. In particular, when the wavelength of the recording laser beam is shortened to narrow the track pitch and high density is required, there is a further problem. Further, since the dye is decomposed during recording to reduce the refractive index and absorption coefficient of the recording layer, it is difficult to obtain a large degree of modulation with a small deformation, that is, to efficiently use the phase difference. A system having a polymer binder in the recording layer has the same problem.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have formed wavelengths of 620 nm to 690, each of which forms a good minute recording portion for realizing high density recording and has a sufficient recording modulation degree.
The present invention has been achieved as a result of extensive studies on a medium and conditions suitable for recording at a short wavelength of nm. The gist of the present invention is, on a transparent substrate having a guide groove, at least a recording layer containing a light absorber,
A wavelength of 620 nm to 690 n from the transparent substrate side is applied to an optical recording medium in which a metal reflective layer containing gold or silver as a main component is sequentially stacked.
m of laser light is incident, the thickness of the recording layer is changed by 10 to 30% by the laser light condensed on the guide groove, and a phase difference of the laser light reaching the reflective layer is generated, and the amount of reflected light due to the phase difference. Of the recording layer of the optical recording medium having a glass transition point of 50 ° C. or higher and a main weight loss onset temperature higher than 250 ° C. or a glass transition temperature of less than 50 ° C. and a main weight loss. Start temperature is 100 ~
It is a layer composed of a resin and an organic dye at 250 ° C., or the main weight loss starting temperature is 150 to 270 ° C., and the weight loss in the temperature range of the main weight loss starting temperature to (main weight loss starting temperature + 100 ° C.) is 20 to 40. % Of the organic dye.

In the present invention, as the optical recording medium, a recording layer made of only an organic dye or a polymer layer containing an organic dye is used. This recording layer is deformed by the heat generated by the absorption of the recording laser light of the light absorber, and as a result, the depth of the groove formed by the reflective layer is apparently changed to change the phase difference. Then, the modulation degree of recording is obtained. To use the phase difference,
It is necessary to adjust the amount of the light absorber so that the amount of transmitted light of the entire recording layer can be secured. Many papers have been published on the calculation of the amount of reflected light that has entered the guide groove. For example, J. Opt. Soc. Am. 69 (1), (19
79), p4, and IEICE Transactions C-1, Vo
l. J72-C-1, No. 2,86, ibid. J7
3-C-1, No. 9 p551 and the like, but especially regarding the calculation of the reflected light amount of the light incident on the guide groove from the substrate side, the Institute of Electrical Communication, J66-C No. 5 p. Three
85 to 392 is practical.

According to this, the phase due to the change of the groove depth
Due to the difference, the reflected light amount is represented by the following formula. I-R₀ ²(1-σ)²+ 2aR₀ ²σ (1-σ) cos
(2knd) + a²R₀ ²σ ²+ 4σR₀* {AR₀co
s (2knd) -R₀} * [Β₁Sinc (2πσ) +
β₂Sinc (πσ)] + 2σ²{A²R₀ ²-2aR₀ ²
cos (2knd) + R₀ ²} * [2β₁Sinc (2π
σ) + 2β₂Sinc (πσ) + β₁{Sinc (π
σ) + Sinc (2πσ)}²+ Β₂Sinc²(Π
σ)]]

Here, R ₀ = complex reflectance of the recording layer in the unrecorded groove portion, aR ₀ = complex reflectance of the recording film in the recording portion, σ =
γ / p, where n = refractive index of the recording layer and k = 2π /
λ, d = groove depth, p = track pitch, γ = groove width, λ =
Wavelength, Sinc (πσ) = sin (πσ) / πσ, β ₁ = 2 / π [cos ⁻¹ (λ / (p · NA)) − 0.5
sin {2con ⁻¹ (λ / (p · NA))}], β ₂ = 2 / π [cos ⁻¹ (λ / (2p · NA)) − 0.
5sin {2cos ^-1 (λ / (2p · NA))}].

As a condition for the above equation to hold, λ / p
The condition <NA <1.5λ / p is required. If it deviates from this range, the interference between the 0th-order light and the 1st-order light is insufficient, and the change in the reflectance cannot be caused by the phase difference. FIG. 1 shows the correspondence between the above symbols and the shape of the disc.
FIG. 1 is a diagram showing the relationship between these parameters and the disk portion, where 1 is a reflective layer, 2 is a recording layer, and 3 is a substrate. FIG. 2 is a graph showing the relationship between the groove width γ at the groove depth d and the reflectance. FIG. 3 is a graph showing the relationship between the film thickness of the recording layer and the reflectance. In FIG. 3, the refractive index n of the substrate is 1.58, the extinction coefficient k is 0.0, the dielectric layer n is 2.1, k is 0.0, the film thickness is 900Å, and the recording layer n is Is 1.5, k is 0.1, n of the silver reflective layer is 0.14, k is 4.15, and the film thickness is 1000Å. When a dielectric layer thinner than 1000 angstrom is formed between the substrate and the recording layer by the sputtering method, the film thicknesses of the groove portion and the groove portion are substantially equal to each other, and the groove shape traces that of the substrate. Therefore, it is estimated that the contribution to the phase difference in that case is small.
By calculation of the above equation, for example, as shown in FIG.
680 nm, p = 1.6 μm, NA = 0.55, n =
1.5, a = 1, γ = 0.6), and the amount of light reflected from the groove changes greatly due to the change in the film thickness of the recording layer due to recording. Usually, as the disc characteristics, when the reflectance is I, I / (R ₀ ² ) = 0.5 or more (I / (R ₀ ² ) = 0.5 to 1.0 before and after recording). When it changes to, the modulation factor is 50%.)

For example, when a film is formed so that the depth (d) of the groove portion of the reflective layer before recording is 900 angstroms, the reflectance I is formed by the projection of 200 angstroms due to the irradiation of the laser beam. / (R ₀ ² )
From 0.244 to 0.428, and a reflectance modulation degree of 43% is obtained. Further, when the film is formed so that the groove depth of the reflective layer before recording becomes 251 angstrom before recording, 449 angstrom by irradiation of laser light,
Due to the formation of the recess of 734 Å, the reflectance I / (R ₀ ² ) is 0.902 to 0.42.
From 8, 0.902 to 0.194, 53 each
%, A reflectance modulation degree of 79% is obtained.

On the other hand, if the change in reflectance due to the change in film thickness is large, the film thickness margin during film formation is small, and it becomes extremely difficult to obtain uniform reflectivity. Therefore,
Usually, a disk is formed by selecting a film thickness (region A in FIG. 3) in which the reflectance change is as small as possible among the film thicknesses shown in FIG. For example, when a recording layer in which a dye is dissolved in a resin is used, as shown in FIG. 3, the recording layer has a reflectance of 10% or more which enables tracking of reproduction, and the recording layer has a film thickness of 900 angstroms to 3000 angstroms. If it is within the range, the change in film thickness before and after recording is 10 to 30% of the film thickness.
In many small cases, that is, the reflectance modulation degree obtained by the convex formation of 200 to 800 angstrom is about 40% at the most, and 50% which is preferable as a disc.
It is difficult to obtain the above modulation degree. Further, when the recording layer is a layer made of a dye, an example thereof is shown in FIG.
Is 1.58, k is 0.0, n of the recording layer is 3.0, k is 0.27, n of the silver reflective layer is 0.14, k is 4.15, and the film thickness is 1000Å. ), The refractive index n is large, and the reflectance change with film thickness is much steeper than in FIG.
The reflectance modulation degree obtained by the deformation of 300 angstroms (30% of the film thickness) in the film thickness of 900 angstroms (region B in FIG. 4) is 42% at most. If the dye does not decompose and the recording portion has the same n and k, if the region B ′ having a large phase difference is used as a condition, the phase difference between the returning light of the recording portion and the non-recording portion is π. In the case of 1, the return light from the recording section is almost eliminated, and a very large recording modulation degree can be obtained. The film thickness change at that time is 500 Å (56% of the film thickness) in FIG. 4 (region B ′).

However, in practice, when a dye monolayer having a large n and k is used as the recording layer, the dye is decomposed by the irradiation of recording light and n and k are reduced, As shown in FIG. 5, the phase difference before and after recording is often small. Therefore, even in the case where the recording layer is a layer made of an organic dye as in the present invention, by using one having a small n value of about 1.5 to 1.9 in the unrecorded state, the influence on the phase difference due to the decomposition of the dye Is small, and a sufficiently large recording modulation degree can be obtained.

Further, when recording is performed not between the guide grooves but between the guide grooves (on the land), the phase difference can be detected in the same manner, but since scattering due to the shape change is easily observed at the same time, the guide Recording on the groove is preferred. In the present invention, the convex portion or the concave portion may be formed by the irradiation of the recording light. Recording is performed by irradiating a high power pulsed light on the guide groove for a short time. When the recording layer contains a resin, the recording layer is heated to a temperature above the melting point of the resin or above the glass transition temperature. In the case of a single dye layer, the amount of the light absorber and the film thickness of the recording layer are adjusted so that the organic dye is heated to a temperature above the main weight loss start temperature, and a reflective layer is further laminated thereon. A high recording modulation degree is obtained by utilizing the change in the phase difference due to the convex portion or the concave portion of the recording portion formed on the guide groove.

In the present invention, a known material such as polycarbonate, polymethacrylate, amorphous polyolefin, or glass is used as the transparent substrate and has a guide groove for servo. It is preferable that the depth of the guide groove is 1000 to 3000 angstrom and the groove width is 0.4 μm or more and half or less of the groove pitch. The groove shape may be a V groove or a U groove.

Depending on the purpose, a dielectric layer is laminated on the substrate. In particular, when the recording layer contains a resin, the substrate is often attacked by the solvent, so that a dielectric layer is necessary to prevent this. In the case of a dye monolayer, it may or may not be present, but it is preferably provided to more effectively utilize the interference effect. Dielectric layer is SiO ₂ , Z
_{nS-SiO 2, ZnS, TaOx} , Al 2 O 3, Y 2
A known material such as O ₃ is used, and its film thickness is preferably 500 angstroms or more. If the thickness is less than 500 Å, the substrate such as polycarbonate may be deteriorated by the diluent solvent of the deformation layer. Further, the dielectric layer also has a function of preventing the recording layer from generating heat and softening and deforming the substrate material as a result of light absorption. Further, in order to increase the reflectance of the disc, dielectric layers may be laminated to form a dielectric mirror.

When the recording layer contains a resin, preferably, a resin composed of a hard segment and a soft segment, that is, a thermoplastic elastomer and an organic dye contained therein are mixed with chloroform, chlorobenzene and cyclohexanone. It is obtained by spin coating a solution diluted with a polar solvent such as dimethylformamide. Further, in the case of a layer composed of an organic dye, it is obtained by spin coating a solution in which the organic dye is dissolved in a solvent such as ethanol, 3-hydroxy-3-methyl-2-butanone, diacetone alcohol, or a fluorinated alcohol. . Generally, the film thickness of the recording layer is preferably about 900 to 3000 angstroms. If it is less than 900 angstroms, it is difficult to obtain good recording sensitivity because it is too thin. If it exceeds 3000 angstroms, the guide groove is completely filled, and the phase difference due to the groove shape cannot be used, resulting in a large recording with a slight deformation. It becomes difficult to obtain the degree of modulation.

The thermal characteristics of the resin and organic dye forming the recording layer greatly affect the recording characteristics. In order to obtain sufficient properties, the resin should have a glass transition temperature of 50 ° C. or higher and a main weight loss starting temperature of higher than 250 ° C. or a glass transition temperature of less than 50 ° C. and a main weight loss starting temperature of 100 ° C. or higher.
It is preferably 0 ° C. or less. If the glass transition temperature is lower than 50 ° C, deformation (irregularities) around the recording portion may be flattened in an environment of 50 ° C or higher, and there is a problem in weather resistance. Further, when the glass transition temperature is lower than 50 ° C., it is used to form the unevenness of the recording portion by the decomposition of the resin itself. In that case, when the main weight loss starting temperature is lower than 100 ° C., the reproduction is performed. It may be decomposed by irradiation with light, and if the main weight loss starting temperature is higher than 250 ° C., the recording sensitivity is deteriorated, which is not preferable. Further, if the glass transition temperature is 50 ° C. or higher and the main weight loss start temperature is 250 ° C. or lower, it is difficult to obtain uniform deformation due to recording light.
The Tg referred to here is t in the measurement of the dynamic elastic modulus.
Since an δ is the temperature at which the maximum value and tan δ does not have the maximum value depending on the type of resin, the endothermic start temperature in DSC (differential thermal analysis) was taken as the glass transition temperature in that case.

The hard segment constituting such a resin is polystyrene, polyethylene, polyamide, polyester and the like, and the soft segment is polybutadiene, polyisoprene, hydrogenated polybutadiene, ethylene / propylene copolymer rubber, natural rubber and the like. It is preferably exemplified. These hard segments agglomerate due to intermolecular force and hydrogen bond to form mechanical lattice points to maintain the shape. On the other hand, the soft segment is non-aggregating, and when heated at a temperature of room temperature or higher, vibration, rotation, and translation modes are excited, but the hard segment suppresses the flow. This soft segment is involved in controlling the size of the shape. The recording layer contains an organic dye as a light absorber in such a thermoplastic elastomer because the light absorption causes the thermoplastic elastomer to be heated and deformed. This dye is also applied to the case where the recording layer is a single dye layer, but a dye whose main weight loss starting temperature is 150 ° C. to 270 ° C. is used. 150
When the temperature is lower than ℃, there is a possibility that the recording state is approached by continuous reproduction, and when the temperature is higher than 270 ° C., the recording sensitivity is deteriorated in the case of the dye single layer. Further, when the dye single layer is used as the recording layer, the main weight loss start temperature to (main weight loss start temperature + 10
An organic dye whose weight loss in the temperature range up to 0 ° C.) is 20 to 40% is used. If the weight loss is less than 20%, it becomes difficult to obtain a deformation amount of 10 to 30% that contributes to the phase difference, and the recording modulation degree may be too small.
If it exceeds, the amount of deformation may spread widely to the peripheral portion.

The term "main weight loss starting temperature" as used herein means the starting temperature of the first weight loss process in which the weight loss exceeds 20% in the TG curve of the TG (thermogravimetric analysis) -DTA (differential thermal analysis) curve. This weight reduction start temperature is determined by the differential thermal balance (Seiko Denshi Kogyo) SSC5200H series TG-DTA-3.
Sample weight of 5 mg at 20 in nitrogen atmosphere at a heating rate of 20 ° C.
6 / min, and as shown in FIG. 6, d ₁ −d showing weight loss
It is the temperature obtained from the intersection of the _two tangents and the ab tangent.

As the organic dye, for example, a metal-containing azo dye, a dibenzofuranone-based dye, a metal-containing indoaniline-based dye, or the like can be used. Even if these organic dyes are used alone, two or more kinds are mixed. You may use it. In the case of an organic dye single layer, the weather resistance may be a problem due to the problem of adhesion with the metal reflection layer, so it is preferable to provide an intermediate layer. For example, a method of forming triazine thiol by spin coating is adopted. To be done.

The adhesion between the resin used in the present invention and the metal reflective layer is extremely good. The reflective layer is a metal film that efficiently reflects the laser light that has passed through the recording layer.
A metal reflective film containing gold or silver as a main component is used because the reflectance does not decrease at m to 690 nm. The thickness of the reflective layer is preferably 600 angstroms or more, and is preferably such that the deformation of the recording layer is not suppressed excessively and the recording sensitivity is not deteriorated too much. Depending on the purpose, a dielectric layer on the reflective layer, or U with a small elastic modulus is used.
You may laminate | stack a V hardening resin layer.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Groove depth 1900 Å, Groove width 0.4 μm
A tantalum oxide film having a refractive index of 2.1 is formed on a polycarbonate substrate having a U-shaped guide groove (1.6 μm pitch) to a film thickness of 90.
Sputtering to 0 Å, 0.1 g of styrene-ethylene / butylene-styrene block copolymer having a number average molecular weight of 71,000 was dissolved in 2.5 g of chloroform (CHCl ₃ ), and 0 0.009 g of cyanine dye (Nippon Photosensitive Dye NK-2929 main reduction start temperature 258 ° C.) and 0.016 g of cyanine dye (Nippon Photosensitive Dye main reduction start temperature 230 ° C.) were mixed, and further diluted twice with cyclohexanone. The resulting solution was spin-coated to form a recording layer. At that time, the film thickness of the groove portion is 3000 angstroms, and the refractive index n and the extinction coefficient k of the recording layer single layer at 680 nm are respectively 1.
It was 5 and 0.1. Gold was sputtered on the recording layer to a thickness of 600 Å.

The glass transition temperature (point on the high temperature side among the temperatures at which tan δ has a maximum) of the resin constituting this recording layer was 100 ° C., and the main weight reduction start temperature was 412 ° C.
A semiconductor laser with a wavelength of 680 nm (N
When evaluated by an A = 0.55) evaluation device, the reflectance modulation degree of the recording portion was 54%. The groove depth of the recording portion of this disk was 800 Å as measured by STM, and the groove depth of the recording portion was about 1100 Å (concave of 300 Å, deformation of 10% of film thickness). When this change in film thickness was read only by the film thickness reflectance, the reflectance modulation degree was 22%, which was much lower than the actual modulation degree.

Example 2 The disk of Example 1 was changed to a disk having n and k of 1.5 and 0.4 by changing the dye amount. Using the evaluation machine of Example 1, the linear velocity was 3 m / s. When recording was performed on the groove with a recording frequency of 500 kHz, a pulse width of 170 ns, and a recording power of 9 mW and reproduction was performed with a reproduction power of 0.8 mW, the carrier level was −20.8 dB and the noise level was −50.2 dB. The signal strength of the land adjacent to this recording portion is such that the carrier level is -40.9 dB and the noise level is -5.
It was 4.5 dB, and a good recording portion which did not spread so much laterally was formed.

[0026]

By utilizing the phase difference, it is possible to form a good minute recording portion for realizing high density recording, and to obtain a large recording modulation degree even if the film thickness change before and after recording is small. Can have a wavelength of 620 nm to 690
A recording method suitable for short wavelength recording of nm is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between each parameter and a disc portion.

FIG. 2 is a graph showing the relationship between the groove width γ at the groove depth d and the reflectance.

FIG. 3 is a graph showing the relationship between the film thickness of the recording layer and the reflectance.

FIG. 4 is a graph showing a film thickness, a phase difference, and a reflectance of a recording layer.

FIG. 5 is a graph showing the film thickness, phase difference, and reflectance of the recording layer after erasing.

FIG. 6 is a chart diagram of a differential thermal balance for determining a main weight reduction start temperature.

[Explanation of symbols]

 1 reflective layer 2 recording layer 3 substrate

Claims (1)

[Claims] 1. A wavelength of 620 nm from the transparent substrate side of an optical recording medium in which at least a recording layer containing a light absorber and a metal reflective layer containing gold or silver as a main component are laminated in this order on a transparent substrate having guide grooves. Inject laser light of ~ 690nm,
The thickness of the recording layer is reduced to 1 by the laser beam focused on the guide groove.
An optical recording method of causing a phase difference of laser light reaching a reflective layer by changing 0 to 30% and reading a change in the amount of reflected light due to the phase difference, wherein the recording layer of the optical recording medium has a glass transition point 50 ℃ or more and the main weight loss start temperature is 250 ℃
Higher resin, or a layer having a glass transition temperature of less than 50 ° C. and a main weight loss starting temperature of 100 to 250 ° C. and an organic dye, or a main weight loss starting temperature of 150 to 270 ° C. An optical recording method, which is a layer comprising an organic dye having a weight loss of 20 to 40% in a temperature range of weight loss start temperature to (main weight loss start temperature + 100 ° C).