JPH07320303A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high density information recording medium which can deal with a laser light source of short wavelength and mark edge recording by setting a coefficient of thermal conduction within a specified range for each of a dielectric layer, a recording layer and a reflective layer laminated on a substrate. CONSTITUTION:A first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are laminated sequentially on a transparent substrate. The coefficient of thermal conduction, defined by the product of thermal conductivity and the film thickness, is set at 0.03-0.1, 0.01-0.03 and 4-12muH/K, respectively, for the first dielectric layer, the second dielectric layer and the reflective layer. It is set preferably at 5-20W/mK for the recording layer. This structure suppresses fluctuation in the length of mark due to laser power resulting in a high density recording medium suitable for mark edge recording.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for recording information such as video, audio, or computer data by using an optical signal from an energy beam such as laser light. And preferably, it relates to a magneto-optical recording medium using a magneto-optical recording layer as a recording layer.

[0002]

2. Description of the Related Art Various researches and developments have been carried out on optical recording media as high-density and large-capacity information recording media, and some of them have been put to practical use. There is a magneto-optical recording medium as one of the optical recording media. In this magneto-optical recording medium, a rare earth-transition metal amorphous alloy film having an easy axis of magnetization perpendicular to the film surface is widely used as a recording layer provided on a transparent substrate.

The recording layer made of this amorphous alloy magnetic film is
There is a problem that durability alone is poor, and a sufficient C / N (carrier signal / noise) ratio cannot be obtained during reproduction. Therefore, some proposals have been made to improve those characteristics. One of them is a four-layer structure medium in which a first dielectric layer, a recording layer, a second dielectric layer, and a metal reflection layer are provided on a substrate.

Further, in such an optical recording medium, information is recorded on the medium by irradiating an energy beam such as a laser beam. At that time, as a laser light source, it is possible to obtain strong energy with a minute volume of 780 n.
An m-wavelength semiconductor laser is often used.

In the past, so-called "mark position recording" has been widely used, in which recording marks having different optical characteristics are formed on the recording layer, and "0" or "1" of digital information is made to correspond to the center of the recording mark. Has been done.

However, as the amount of information increases, the recording capacity of the information recording medium is required to increase. for that reason,
It is necessary to reduce the recording mark length by shortening the wavelength of the laser light used, the space between marks, and the density between adjacent tracks.

Further, instead of the conventional mark position recording, "mark edge recording" in which information "0" or "1" is made to correspond to both ends of the recording mark and the recording capacity is 1.5 times the mark position is adopted. Are also being considered.

Alternatively, a multi-layered structure such as a writing layer and a reading layer or an intermediate layer is adopted as the recording layer, and the difference in thermomagnetic characteristics is utilized to partially record the recording marks on the writing layer in the reading layer. A so-called super-resolution technique has also been proposed in which a minute recording mark can be read by using a magnetic mask.

[0009]

In order to increase the recording capacity, that is, increase the recording density, the recording mark reduced as described above is recorded clearly and at an accurate position with an accurate size. Required to do. That is, when recording with the same power, the linearity between the recording pulse width and the recording mark length is good, when recording with the same pulse width, the recording power dependence of the recording mark length is small, and between adjacent marks Small thermal interference is required.

Particularly in mark edge recording, the edge corresponds to recording information. Therefore, the accuracy of the position is required more severely than the conventional mark position recording. Therefore, the problem of thermal interference between adjacent marks becomes an important issue.

Therefore, it is important to control the distribution of heat generated in the recording layer by laser light, that is, to suppress the spread of heat. It is conceivable that the dielectric layer and the reflective layer that sandwich the recording layer are made completely heat insulating materials so that heat is applied only to the recording layer. However, suppressing the diffusion of heat in the thickness direction promotes the in-plane expansion of heat in the recording layer. In addition, the recording layer may be deteriorated due to heat, and the service life may be shortened. Therefore, it is an issue to control the heat transfer in the thickness direction and the heat transfer in the in-plane direction to the optimum state.

Further, even in the super-resolution technique, the accuracy of the mark position and the mark shape is required to read the signal from the masked small area. In order to make full use of the difference in thermomagnetic characteristics of each layer of the multilayer structure, the recording temperature is quickly raised, but it is difficult to raise the recording temperature higher than that, and there is no bleeding of the mark shape to the surroundings. is necessary.

An object of the optical recording medium of the present invention is to solve the above problems and to obtain a high density information recording medium which can be applied to a short wavelength laser light source and can be applied to mark edge recording.

[0014]

The optical recording medium of the present invention comprises:
On the transparent substrate, the first dielectric layer, the recording layer, the second dielectric layer,
In the optical recording medium which is provided with a reflection layer and a reflection layer in this order and records information by using an optical signal, the thermal conductivity coefficient defined by the product of thermal conductivity and film thickness is 0.03 to 0.1 for the first dielectric layer.
.mu.W / K, the second dielectric layer is 0.01 to 0.03 .mu.W / K, and the reflective layer is 4 to 12 .mu.W / K.

As described above, for mark edge recording, accurate control of the edge position is necessary, and control of heat distribution is important. However, good C in optical recording media
In order to obtain / N, there are optical restrictions on the medium configuration. That is, in order to concentrate the laser beam on the recording layer and amplify the optical signal from the recording layer, the film thickness, the refractive index, and the absorption coefficient of the first dielectric and the second dielectric, and the reflectance and the absorption of the reflective layer. Optimal conditions are selected according to the light source for which the coefficient is used, that is, the laser light wavelength.

In order to obtain more signal light from the recording layer, the absorption coefficient of the dielectric layer is low in the wavelength range of the light source used,
The closer to zero, the better. The higher the reflectance of the reflective layer, the better. Alternatively, in order to concentrate the light on the recording layer and amplify the signal light from the recording layer (enhancement of the Faraday effect), the light interference effect of the first dielectric layer and the second dielectric layer is used. In order for this to work effectively, the refractive index of the dielectric layer must be 1.6 or more.

Further, the production of the medium is usually performed by a process using a vacuum such as a sputtering method. At that time,
In order to reduce the manufacturing cost, it is necessary to increase the throughput in the vacuum device. Therefore, it is preferable to use a thin constituent film because the productivity is higher.

As a result of these, the film thickness required for the dielectric layer naturally falls within a certain range depending on the type of laser light source used. For example, when a laser having a wavelength of 680 nm is used as a light source and the refractive index of the dielectric is about 2, the first dielectric layer has a thickness of 40 to 140 nm and the second dielectric layer has a thickness of 5 to 60 nm. This range depends on the wavelength of the light source used as described above.

Under such optically determined constraint conditions, how accurately the edge position of the mark recorded on the recording layer is controlled is the key to obtaining a high density medium. Therefore, when a recording signal is given by optical energy, the recording layer has a heat insulating property that easily rises rapidly to the recording temperature, and exhibits heat dissipation that prevents the temperature from becoming higher than the recording temperature. Medium is preferred.

As the dielectric layer of the present invention, a material having a low thermal conductivity is preferable. Conventionally, Si is generally used as a dielectric layer.
N, AlN, SiC, etc. are used. But for example Si
The thermal conductivity of N film is as high as 3 W / mK, and materials with low heat insulating properties have been used. Or 24.9W / m with AlN film
Dielectric materials with high thermal conductivity of 10 W / mK are used for K and Si ₃ N ₄ films.

Therefore, the dielectric layer having the characteristics required in the present invention is mainly composed of Al, Si, and N atoms, and contains 30 atoms of one or more kinds of atoms selected from C, O, and H.
It can be realized by making it contained within%. That is, although the dielectric layer made of Al, Si, and N atoms shows a decrease in thermal conductivity due to lattice scattering due to an increase in the types of constituent atoms, C,
A covalent bond is formed by adding one or more elements selected from O and H, and the number of the covalent bonds is limited, so that heat transfer due to lattice vibration is blocked and the thermal conductivity is lowered. can get.

Of course, if the thermal conductivity of the dielectric layer is only low, heat may be accumulated in the recording layer and the durability may be reduced. Therefore, it is necessary to appropriately transfer heat to the reflective layer, and the dielectric layer needs to have a heat transfer coefficient within the range of the present invention.

When a dielectric layer having a high oxygen content is used, the oxygen composition near the recording layer is reduced in order to prevent the recording layer from being oxidized, and a composition distribution in the film thickness direction is formed. It is also possible to use a method in which the dielectric layers are multilayered. In this case, the thermal conductivity coefficient of the entire dielectric layer needs to fall within the range of the present invention.

As a method of forming these dielectric layers, for example, known vacuum deposition, sputtering method, CVD method and the like are used, but the sputtering method is used because of the ease of forming a uniform film. In this case, a metal alloy, an oxide, a nitride, a carbide, or the like can be used as the target. Further, the atmosphere gas at that time is Ar, X
In addition to the inert gases of e and Kr, gases that react in plasma such as nitrogen, hydrogen, oxygen, carbon dioxide, carbon monoxide, nitrogen monoxide, nitrogen dioxide, methane gas, ethane gas, and silicon hydride gas are selectively mixed. Thus, a dielectric layer having a desired composition can be obtained.

On the other hand, with respect to the reflective layer, even if the thermal conductivity thereof is low, the effect similar to that of increasing the thermal conductivity can be obtained by increasing the film thickness. However, although an increase in the film thickness of the reflective layer is certainly effective in optimizing the recording sensitivity, it is not effective in accurately controlling the mark position, and a thin film is preferable. This is because as the film thickness of the reflective layer increases, heat is accumulated in the reflective layer and heat radiation from the surface is delayed. Therefore, it is necessary to combine the reflective layer having the thermal conductivity coefficient of the present invention and the dielectric layer.

The lower limit of the film thickness of the reflective layer is preferably about 20 nm or more in order to obtain an optically sufficient reflectance. The upper limit of the film thickness is preferably determined in consideration of productivity and stress generated in the film.

The reflective layer also radiates the heat transferred through the dielectric layer to prevent an excessive temperature rise of the recording layer. Therefore, as the reflective layer, a film having high thermal conductivity is preferable, and a film having 80 W / mK or more is preferable.

The reflective layer having a thermal conductivity of the present invention contains {Ti, Cr, Ta, Co as a main component and contains at least one element selected from the group of {Al, Au, Ag, Cu}. , Ni, Mg, S
An alloy film in which an element selected from the group i) is added at 10 atom% or less, or a multilayer film thereof is preferable. Such a reflective layer is formed by a known vapor deposition, sputtering method or the like.

Further, the recording layer of the present invention may be any thin film layer as long as it converts light into heat to record information. For example, a phase change recording layer and a magneto-optical recording layer are typically used. In particular, recording and reproduction by the magneto-optical effect
Those that are erased are preferably used. As the magneto-optical recording layer, a known rare earth-transition metal alloy film, a multilayer film using exchange coupling, an artificial lattice multilayer film of Pt / Co, etc. can be used.

However, considering the heat transfer in the recording layer, it is preferable that the thermal conductivity of the recording layer is in the range of 5 to 20 W / mK. Particularly preferably, a recording layer mainly containing a rare earth-transition metal is used. The thickness of this recording layer is selected within a range not exceeding 200 nm for both single layer and multilayer.

Further, in order to improve the durability of this medium, it is generally practiced to further provide a protective layer on the reflective layer, but the formation of the protective layer may affect the thermal characteristics. For this reason, as the protective layer to be used, an organic polymer material having a good heat insulating property and a small thermal conductivity is used, and preferably the thermal conductivity is 0.2 W / mK or less and the film thickness is 5 to 5
The one with 10 μm is used.

As the substrate of the present invention, any substrate such as a known polycarbonate resin substrate which is transparent to laser light and has a small birefringence can be used, including a known polycarbonate resin substrate.
The thermal conductivity of the substrate is originally low and a material of 0.2 W / mK or less is used.

[0033]

[Example] 1.2 μm with a disk having a diameter of 90 mm and a thickness of 1.2 mm
A disc substrate (PC substrate) made of a polycarbonate resin having a groove of a pitch was placed in a vacuum chamber of a magnetron sputtering apparatus capable of installing 3 targets. The target for the dielectric layer is 100 mm in diameter and 5 mm in thickness.
A disk made of AlSi sintered body was used. A TbFeCo (19: 72: 9) alloy target was used as the target for the recording layer. The target for the reflective layer is AlAu (9
8: 2) An alloy target was used. The values in parentheses for alloys are composition ratios (atom%) corresponding to the order of element names.
Represents

First, the tank was evacuated to a pressure of 50 μPa. Next, a mixed gas of Ar / N ₂ (Ar: N ₂ = 90:
(10 vol%) is introduced into the vacuum chamber and hydrogen gas
Add 20 vol% to Ar / N ₂ mixed gas and set the pressure to 1.
Adjusted to 33Pa.

Discharge power 500 W, discharge frequency 13.56
Rotating PC with high frequency sputtering at MHZ
An AlSiN: H film having a thickness of 70 nm was deposited as a first dielectric layer on the substrate. The composition of the AlSiN: H film formed here is the Auger electron spectrometer (SAM610 by PHI), FT
As a result of analysis using an IR analyzer (manufactured by Shimadzu Corporation), the film contained 12 atom% of hydrogen.

Then, using a TbFeCo alloy target, Ar
DC sputtering was performed under the conditions of a gas pressure of 0.5 Pa and a discharge power of 150 W, and TbFeCo (20.5: 70.9:
8.6) An amorphous alloy film was deposited to a thickness of 22.5 nm.

Subsequently, as a second dielectric layer, only the film thickness is changed under the same conditions as the first dielectric layer, and AlSiN:
An H film was deposited to 20 nm.

Next, using an AlAu alloy target, Ar gas pressure
DC sputtering with a discharge voltage of 125 W at 0.2 Pa 40
nm AlAu alloy film was deposited. Au content is 2.2 atom%
Met.

The produced magneto-optical medium was a magneto-optical recording / reproducing apparatus (DDU-1000 manufactured by Pulstec Industrial Co., Ltd.),
The recording / reproducing characteristics were measured under the following conditions, and the fluctuation range of the mark length when the laser power fluctuated was measured from the laser power dependence of the recording mark length.

Laser wavelength used = 680 nm, NA = 0.55.
Recording conditions: desk rotation speed = 3000 rpm, recording track position = radius 30 mm, minimum recording mark length T = 0.34 μm, applied magnetic field during recording = 250 Oe, recording signal pattern = 2 T (M),
8 T (S), 4 T (M), 8 T (S), 8 T (M), 8
T (S) (S = space, M = mark). Playback conditions: Desk rotation speed = 3000 rpm, read laser power = 0.6 m
W.

The laser power was changed to measure the laser power dependence of the reproduction mark length (4 L, 8 L) of the 4 T and 8 T recording marks, and recording was performed with the laser power (Pw) at which 4 T = 4 L. From the length of 8 L when played back (8 T-8 L) / T × 10
The variation width of the mark length was set to 0%. Table 1 shows the shift fluctuation range when Pw changed by + 10%. The smaller the shift variation width, the smaller the variation of the recording mark length, that is, the edge position.

The thermal conductivity of the dielectric layer and the reflective layer was measured using a thin film thermal conductivity measuring device (manufactured by Vacuum Riko Co., Ltd.) by depositing each film alone on a quartz thin plate to a thickness of about several μm. did. Table 1 shows the thermal conductivity coefficient (film thickness × thermal conductivity) of each layer based on the thermal conductivity of each film.

[0043]

[Comparative Example] The same as Example 4 except that the following conditions were changed.
A medium having a layer structure was prepared. That is, for the dielectric layer, an AlSiN film was deposited without adding hydrogen gas at the time of manufacturing. As the reflective layer, the target was AlAuTi (92.0: 4.8: 3.2).
Using an alloy target, depositing an AlAuTi film with a thickness of 40 nm, Au, T
The composition ratio of i was 11 atom%. Table 1 shows the results of evaluation performed in the same manner as in the examples.

[0044]

[Table 1]

[0045]

As shown in Table 1 for the results of Examples and Comparative Examples, in the case of the combination of the dielectric material having the thermal conductivity coefficient and the reflective layer of the present invention, the fluctuation width due to the fluctuation of the mark length due to the laser power varies. It is small and suitable for edge recording, that is, it has the effect of enabling high-density recording.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 11/10 521 J 9075-5D 523 9075-5D

Claims (4)

[Claims] 1. A transparent substrate, a first dielectric layer, a recording layer, and
In an optical recording medium having a second dielectric layer and a reflective layer in this order and recording information using an optical signal, the thermal conductivity coefficient defined by the product of thermal conductivity and film thickness is Body layer is 0.03-0.1 μW / K, second dielectric layer is 0.01-0.03 μ
An optical recording medium characterized in that W / K and the reflection layer are 4 to 12 μW / K. 2. The reflection layer is mainly composed of one or more elements selected from the group of {Al, Au, Ag, Cu} and {Ti, Cr, T.
element selected from the group of a, Co, Ni, Mg, Si} 10 atom%
The optical recording medium according to claim 1, wherein the optical recording medium is an alloy film or a multilayer film added below, and the thermal conductivity of the reflective layer is 80 W / mK or more. 3. The optical recording medium according to claim 1, wherein the recording layer has a thermal conductivity of 5 to 20 W / mK. 4. The optical recording medium according to claim 1, wherein the recording layer is a magneto-optical recording layer.