WO2003003361A1

WO2003003361A1 - Optical recording medium

Info

Publication number: WO2003003361A1
Application number: PCT/JP2002/006440
Authority: WO
Inventors: Yuichi Sabi; Takashi Iwamura; Sakuya Tamada
Original assignee: Sony Corporation
Priority date: 2001-06-27
Filing date: 2002-06-26
Publication date: 2003-01-09
Also published as: JPWO2003003361A1

Abstract

An optical recording medium comprising at least a metal film (3) and a recording film (4) of an organic pigment material sequentially formed on a substrate (1) formed with recesses (2), wherein a WORM type next-generation optical recording medium comprises recesses having depths selected to be 15 nm-50 nm, and has excellent reproducing features including a high reproduction output.

Description

' Specification

Optical recording medium

Technical field

The present invention relates to an optical recording medium, and in particular, aims to improve reproduction characteristics in a phase modulation type optical recording medium. Background art

At present, functional organic color materials are widely used as write-once type optical disc recording materials, and are especially produced in large quantities at low cost as write-once type compact discs (CD-R). In the optical system of DVD (Digital Versatile Disc), the write-once standard has been put together as write-once DV D (DVD-R), and has been released.

Furthermore, as an optical disc of a large-capacity optical recording medium, which is now regarded as a next-generation optical recording medium, recording is performed from the side of the light transmission protection film formed on the recording surface to the recording surface, that is, through the light transmission protection film. Standardization of blue-violet light on the surface and a numerical aperture NA of the objective lens of 0.85 is under study.

By the way, even in this large-capacity optical recording medium, a large-capacity optical recording medium intended for so-called “live recording”, that is, only one recording is performed, and the recording is stably maintained for many years without being erased. There is an increasing need for a write-once, large-capacity optical recording medium that can be used. In the standards examined for the large-capacity optical recording medium described above, the recording film is based on a phase-change material, but as a recording film for a write-once-type large-capacity optical recording medium, as in CD-R. In addition, it is desirable to use an organic dye material in order to simplify the production and reduce the cost.

However, in such a recordable large-capacity optical recording medium, However, there is a problem in applying the knowledge of conventional write-once CD-R and DVD-R.

That is, as a light source used in a large-capacity optical recording medium, short wavelength 380 ηπ! The above-mentioned blue-violet light source of up to 450 nm, for example, 450 ± 5 nm, is applied.If the recording film is made of an organic dye material, the characteristics of the organic dye material constituting the recording film may vary. , CD-R and DVD-R, which differ in the optical constants due to the difference in the organic dye material of the recording film, simply the recesses formed in the substrate, for example, a continuous group for tracking or Changing the depth of the intermittent group according to this difference in wavelength cannot optimize for obtaining excellent reproduction characteristics.

Also, the track pitch of a large capacity optical recording medium is much smaller than that of a conventional optical recording medium. For example, while the track pitch in CD is 1.6 m, the track pitch in a large-capacity optical recording medium is, for example, about 0.0Sβm. In this case, the problem is the inclination of the side wall of the tracking dull formed on the disk substrate.

The formation of concavities and convexities of groups or pits in a normal CD or the like is achieved by injection molding using a stamper having a concavo-convex pattern corresponding to the groups or pits in the production of a disc substrate, and the 2P method (Photopolymeri zation method). ) And the like.

This stamper is manufactured by mastering, that is, by mastering using a photo resist. Pattern exposure on the photo resist in this master ring usually uses blue light or ultraviolet light. . However, in the case of a narrow track pitch, as in the above-described large-capacity optical recording medium, the pattern exposure by light described above causes the side wall surface of the group to form a gentle slope. Pine.

Therefore, pattern exposure for the photo resist is performed by electron beam lithography, or the spot diameter is reduced by using a so-called two-field configuration in which a condenser lens is placed close to the exposure surface in the optical system. However, there has been no improvement in the reproduction output, such as a method of steepening the side wall surface of the group. Disclosure of the invention

An object of the present invention is to provide an optical recording medium having excellent reproduction characteristics including high reproduction output in the above-mentioned write-once large-capacity optical recording medium.

The optical recording medium according to the present invention is formed by forming at least a metal film and a recording film made of an organic dye material on a substrate in which a concave portion is formed. An optical recording medium on which at least reproduction is performed, and the depth of the concave portion is 15 ηπ! ~ 50 nm.

The organic dye material of the recording film is composed of an organic dye material having a refractive index n of 1.9 or more before recording with respect to light having a wavelength of 380 nm to 450 nm and causing a change in the refractive index after recording. I do. The recording film has the same thickness on both the bottom surface of the concave portion and the upper surface of the convex portion between the concave portions.

According to the optical recording medium of the present invention, an optimum signal output can be obtained in a write-once, large-capacity optical recording medium in which reproduction is performed by the above-described phase modulation method. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional view showing the basic structure of an optical recording medium according to the present invention. FIG. 2 is a cross-sectional view of a concave portion of an optical recording medium for explaining the present invention, FIG. 3 is a diagram showing a relationship between a group width and a signal amplitude for explaining the present invention, and FIG. FIG. 5 is a schematic plan view showing a recording state in the optical recording medium according to the present invention, and FIG. 5 is a diagram showing a reproduction signal level in a track length direction of the optical recording medium for explanation of the present invention.

FIG. 6 is a diagram showing the dependence of the signal amplitude of the optical recording medium on the groove depth for explaining the present invention, and FIG. 7 is a graph showing the reflectance and the modulation factor of the optical recording medium for explaining the present invention. FIG. 8 is a diagram showing the group depth dependency, FIG. 8 is a diagram showing the group depth dependency of the signal amplitude of the optical recording medium used for explaining the present invention, and FIG. 9 is used for explaining the present invention. FIG. 4 is a diagram showing the group depth dependence of the reflectance and the degree of modulation of an optical recording medium according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

The optical recording medium according to the present invention can form a write-once, large-capacity optical disk, that is, the numerical aperture N.A. of the optical system is 0.85 ± 0.05, and the wavelength power is 380 nm or more. The configuration is such that a reproduction mode or a reproduction and recording mode using a laser in a blue-violet region of 450 nm can be adopted.

An optical recording medium 10 according to the present invention, as shown in a schematic cross-sectional view of an example in FIG. 1, includes a concave portion 2 on a substrate 1 on which a continuous group for tracking or an intermittent group is formed. A metal film 3, a recording film 4, and a dielectric film 5 are formed, and a light-transmitting protective film 6 on which a light-transmitting resin film having a thickness of, for example, 0.1 mm is formed by a spin coat is formed. It is formed by adhesion. '

The above-mentioned laser beam 9 in the blue-violet region is incident on the optical recording medium 1 Q from the light transmission protective film 6 side via the objective lens 11. In this configuration, the protruding part on the side The concave portion 2 (group) is referred to as the concave portion 2 (group), and the surface between these concave portions 2 on the side close to the laser light 9 incidence surface is referred to as the convex portion 7 (land).

In the present invention, in particular, the depth D of the recess 2 shown in FIG. 2 is set to 15 nm to 50 nm.

The recording film 4 has a characteristic that the refractive index n is 1.9 or more before recording, and is made of an organic dye material that changes the refractive index after recording.

The film thickness of the recording film 4 is formed by, for example, a vapor deposition film having the same film thickness in both the concave portion, that is, the bottom surface of the group 2 and the convex portion, that is, the upper surface of the land 7.

The optical recording medium according to the present invention uses the land as a recording area. This is because, for example, when the organic dye material constituting the recording film is vapor-deposited, the homogeneity of the recording film tends to be impaired in the recesses (groups), and this inhomogeneity causes noise. It is a recording area.

The optical recording medium according to the present invention will be described with reference to examples. For example, considering the optical recording medium with a wavelength of 4.55 ± 5 nm and NA 0.85 ± 0.05, the concave portion 2, that is, the average width W of the group is 0.10 m to 0.14 m. In this embodiment, the average width W is set to 0.14 m.

. In the case of the phase modulation mode, the relationship between the average width W of the concave portion (group) and the reproduction signal amplitude is as shown in FIG. 3, and the average width W at which the reproduction signal amplitude is maximum is 0.10 im to 0.14〃m. To form such a thin group, technical measures are needed at this stage, and the width should be set as wide as possible in this range. The advantage is that even if the average width W deviates slightly from 0.14 m, there is almost no effect on the setting of the depth of the recess. The track pitch is mainly involved in crosstalk, but the purpose of the present invention is to obtain the maximum output. In the present invention, a configuration for realizing this is specifically described. Is configured to set the depth of group 2.

The crosstalk can be made sufficiently small if the phase modulation mode with a narrow group width is used.In this embodiment, the track pitch is fixed to 0.6 m without crosstalk so that the detection signal can be easily evaluated. did.

Further, as described above, since the film thicknesses of the recording film 4 on the bottom surface of the group and the top surface of the land are made equal, they have the same complex reflectance with respect to the reflected light, that is, the returned light from these surfaces. .

That is, the phase information of the reflected light can be the same as the case where the metal reflection film is simply formed. In this state, the tracking error signal obtained from the group has a group depth of 4/4 (specifically, for example, the substrate of the optical recording medium is made of polycarbonate (PC) resin, and the wavelength; I = 400 nm). In, when the group depth is 67 nm), the phase is just shifted.

Therefore, if the amount of reflected light from the land and the group is the same, the reflected light from both will cancel each other out, and the amount of reflected light (return light) will be zero in principle.

Then, a change in the refractive index of the recording film due to recording causes a phase shift in the recording portion. As a result, the return light, that is, the amount of reflected light increases, and the recording is read by so-called Low to High, in which the amount of reflected light changes from the above-mentioned state of zero before recording to the direction in which the amount of reflected light increases.

However, in this case, since the amount of reflected light is zero in an unrecorded state, a focusing / tracking error signal cannot be obtained in a state before recording, and the focusing / tracking cannot be performed. Inconveniences such as inability to apply a servo and incompatibility with other optical recording media arise.

If the depth of the group is made deeper than 67 nm due to the above-described relationship to cope with such inconvenience, a problem arises in that the sidewall 2a is inclined in the formation of the group.

In other words, at present, the inclination tan 0 of the side wall 2a shown in FIG. 2 is 1 to 2, and if the depth of the group is set to be deeper, for example, 100 nm, the average width W of the group is 0 If it is 14 m (140 nm), the land width will be 140 nm, and the slope of the side wall will occupy a considerable area.

As described above, when the proportion occupied by the inclined side wall increases, the signal component from the recording film formed in this portion increases, and the noise increases.

Therefore, it is desirable that the depth of the group, that is, the concave portion 2 be as shallow as possible and that the side wall be as high as possible.

The present invention constitutes an optical recording medium which addresses such a point, and will be described with reference to examples.

(Example 1)

In this embodiment, a substrate 1 having irregularities on its surface is prepared by injection molding using a polycarbonate resin. That is, a concave portion 2 is formed by a tracking guide group having a depth of 20 nm on one main surface of the substrate 1, and a convex portion, that is, a land 7 is formed between adjacent concave portions 2 as a recording portion. did.

On the main surface of the substrate 1 on which the above-mentioned irregularities are formed, a metal film 3 of 30 nm in thickness of Ag is deposited, and a recording film 4 of an organic dye material with a thickness of 25 nm is formed thereon. A dielectric film 5 of 100 nm thick SiN is formed thereon, and a light-transmitting protective film of 100 m thick ultraviolet curable resin is formed thereon. 6 An optical recording medium, that is, an optical disk in this example was produced by coating.

In this example, the dielectric film 5 serves as an isolation layer for preventing the reaction between the recording film 4 and the light-transmitting protective film 6 in an uncured state.

For the recording film 4, the optical constants of the organic dyes are expressed as n (refractive index) for the real part of the complex refractive index and k (extinction coefficient) for the imaginary part.

(N, k) before recording for 405 nm is (2.35, 0.05), and after recording, the organic pigment material triphenylamine changes to (1.5, 0). Derivative was used.

In this case, since the thickness of the metal film 3 was sufficiently large, the reflectance of the recording film 4 before and after recording hardly changed, and the reflectance was about 50% in both cases.

As shown in a schematic plan view in FIG. 4 for the optical disc according to this embodiment, the land 7 has 0.69〃] 1 mark] \ [and 0.69〃m space. This was recorded and reproduced. Figure 5 shows the measurement results of the reproduced signal level.

In this case, the signal level is normalized with the light intensity incident on the optical disc as 1, and the horizontal axis represents the position X in the track length direction.

As can be seen in FIG. 5, when the reproduction laser beam passes through the recording mark M, the phase of the reflected light in the mark M changes, causing interference with the reflected light from the surroundings, and the amount of returned light is reduced. It can be seen that it has decreased. This is basically the same as the CD-R or DVDR-R recording mode. .

Thus, an ideal reproduced signal was obtained.

(Example 2)

In this example, under the same conditions as in Example 1, optical disks were produced in which the depth D of group 2 was changed to 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm. Each light source with these depths D changed Figure 6 shows the signal strength difference between the center of the mark and the center of the space in the reproduced signal due to the disk, that is, the signal amplitude taken on the vertical axis. As shown in FIG. 6, in the film configuration of Example 1, the signal amplitude reaches its maximum value when the group depth D is around 20 nm, and the signal amplitude decreases when the group depth D is smaller or larger. I have.

In other words, it can be seen that the largest modulation depth can be realized when the group depth D is around 2 Onm.

By the way, the reproduction signal characteristics are not optimized only by the signal amplitude. If the reflectivity is too low, focus and tracking servos cannot be applied. However, there is a problem that the shot noise of the light source becomes large and the servo becomes unstable.

In order to avoid such a problem and to apply the servo reliably, a return light amount of at least 10% or more is required.

On the other hand, it is said that it is desirable that the modulation degree of a signal in an optical recording medium, for example, an optical disc be 0.5 or more.

This degree of modulation is obtained by dividing the signal amplitude by the reflectance before recording. If the reflectance is high even if the signal amplitude is large, the return light after recording does not ideally decrease.

Figure 7 shows the results of measuring the depth of the group and the relationship between the reflectance (curve 71) and the modulation (curve 72) before recording.

The reflectivity decreases as the depth of the group increases, as the phase shift before recording approaches 7Γ. It can be seen that in order for this reflectivity to be at least 10% as described above, the depth D of the group should be selected to be at most 40 nm.

The depth D at which the degree of modulation is 0.5 or more is 15 ηm. That is, the depth D of the group, that is, the recess 2 is 15 ηπ! An ideal reproduction signal can be obtained by selecting a wavelength of about 40 nm.

The film thickness of the recording film 4 was about 25 nm in this embodiment, but this film thickness is extremely thin as compared with a film thickness of 200 nm or more in the case of CD-R. Therefore, such a configuration in which a sufficient modulation can be obtained with a thin film thickness is difficult to obtain with a conventional configuration. In other words, according to the present invention, there is an effect that the recording film can be made thin.

(Example 3)

In this embodiment, the return light amount of light irradiation on the optical recording medium is increased.

To increase the amount of return light, the thickness of the metal film 3 may be increased. However, if the thickness is too large, the recess 2, that is, the inside of the group is buried, which causes noise. In this example, the film configuration was changed.

That is, as in Example 1, on a PC (polycarbonate) resin substrate 1 having grooves formed thereon, a 30 nm-thick Ag metal film 3 and an organic dye material 25 nm recording film 4, S

In this embodiment, the dielectric film 5 and the light transmission protection film 6 are formed by 1 N. In this embodiment, the film thickness of the dielectric film 5 by SiN and the organic dye material of the recording film 4 are used. changed. That is, the thickness of the dielectric film 5 is

20 nm, the substrate of the organic dye material of the recording film 4 was made of a triphenylamine derivative, the refractive index n for a wavelength of 450 nm before recording was 2.30, and the extinction coefficient was 0.134.

Figure 8 shows the measurement results of the relationship between the group depth D and the reproduced signal amplitude in this case.

FIG. 9 shows the measurement results of the group depth D and the relationship between the reflectance (curve 91) and the modulation factor (curve 92). As is apparent from FIGS. 8 and 9, the amplitude is almost the same as that of the second embodiment, and the group depth D showing the maximum value is slightly shifted to about 25 nm. However, the reflectivity is generally increased, and the group depth at which the reflectivity is 15% is about 50 nm, and the range where the modulation factor is 0.5 or more is about 25 nm.

That is, an ideal reproduction signal can be obtained by selecting the depth D of the group, that is, the concave portion 2 from 25 nm to 50 nm.

That is, according to the second and third embodiments, the depth of the groove, that is, the concave portion 2 in the substrate 1 is in the range of 15 nm to 50 nm, and an optical recording medium from which a good reproduction signal can be obtained by selecting a film configuration. Is obtained.

That is, according to the present invention, an optical recording medium that can be applied to an optical system having the above-described short wavelength, ie, 380 η 111 to 450 0 11111, and high., Ie, 0.85 ± 0.05, is realized. As a result, high-density recording becomes possible.

Incidentally, in the configuration of the present invention, the optical recording medium is not limited to the above-described embodiment, but can be modified and changed. You can also take

As described above, the optical recording medium using the organic dye material according to the present invention as a recording film can be configured so as to obtain a sufficient reproduction output by selecting the depth of the concave portion of the substrate to be small. In addition, the fabrication of the substrate is facilitated, and the problem of generation of noise due to inclination and roughness of the side wall when the depth of the concave portion is large is avoided.

In addition, since the thickness of the recording film can be reduced to 20 nm on such a substrate, cost can be reduced, throughput can be improved, and cost can be reduced. In addition, the thermal characteristics can be easily optimized, and a film can be formed by vapor deposition. In this way, according to the present invention, an optical recording medium applicable to the above-described short wavelength, high NA optical system can be realized, and high-density recording, that is, a large-capacity optical recording medium can be configured. It can be done.

Claims

The scope of the claims

1. At least a metal film and a recording film made of an organic color material are sequentially formed on a substrate having a concave portion, and at least reproduction is performed by light having a wavelength of 380 nm to 450 nm. Optical recording media

The depth of the recess is selected from 15 nm to 50 nm,

The organic dye material of the recording film is an organic dye material having a refractive index n of 1.9 or more at the wavelength before recording and causing a change in the refractive index after recording,

An optical recording medium characterized in that the recording film has the same thickness on both the bottom surface of the concave portion and the upper surface of the convex portion between the concave portions.

2. The optical recording medium according to claim 1, wherein the recording film is formed by a deposition film of the organic dye material.