JP3173177B2 - Optical recording medium and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information by irradiating light, and a method of manufacturing the same.

In particular, the present invention relates to a rewritable phase-change optical recording medium such as an optical disk, an optical card, an optical tape, etc., which has a function of erasing and rewriting recorded information and capable of recording information signals at high speed and high density. The present invention relates to the manufacturing method.

[0003]

2. Description of the Related Art The technology of a conventional rewritable phase-change optical recording medium is as follows.

[0004] These optical recording media have a recording layer containing tellurium as a main component. During recording, a laser beam pulse focused on the crystalline recording layer is irradiated for a short time to partially melt the recording layer. I do. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. The light reflectance of this recording mark is lower than that of the crystalline state and can be reproduced optically as a recording signal.

At the time of erasing, the recording marks are irradiated with a laser beam and heated to a temperature lower than the melting point of the recording layer and higher than the crystallization temperature to crystallize the recording marks in an amorphous state, and the original unrecorded data is recorded. Return to condition.

In this optical recording medium, a dielectric layer having heat resistance and translucency is usually provided on both surfaces of the recording layer to prevent the recording layer from being deformed and having openings during recording. Further, a metal reflective layer such as Au (gold) having light reflectivity is provided on the dielectric layer on the opposite side to the light beam incident direction to improve the signal contrast at the time of reproduction by an optical interference effect, and to provide a cooling effect. A technique for facilitating the formation of a recording mark in an amorphous state and improving erasing characteristics and repetition characteristics is known (M. Terao et al, SPIE Vol. 1078 p2-10 (1
989)).

On the other hand, as an example of a reflection layer of a conventional write-once type phase change optical disk, there is a reflection layer made of an alloy obtained by adding an additive element such as Ta or Ti to Al (Japanese Patent Laid-Open No. Sho 62).
-137743, JP-A-1-169975, JP-A-2-128332).

[0008]

An object of the rewritable phase-change type optical recording medium as described above is to repeat recording and erasing operations, and to repeat recording and erasing operations. This means that the reproduction signal quality such as characteristics and c / n deteriorates and fluctuates. One of the causes is that the reflective layer of Al or the like undergoes a change in the crystalline state such as coarsening of the crystal grain shape due to the heating and cooling cycles during recording, and the thermal conductivity of the reflective layer and the like also accompany the change. Change, deformation of the reflective layer, or the like, or poor adhesion to the dielectric layer and peeling. Also, during long-term storage, Al
The crystal state of the alloy changes, causing deformation such as hillocks or peeling off from the dielectric layer, causing defects, solid phase reaction at the interface with the dielectric layer such as ZnS-SiO ₂ , and the Al alloy layer. There is a problem such as a decrease in the reflectance of the reflective layer due to oxidation of itself.

An object of the present invention is to provide a reflective layer in which the thermal deterioration due to such repetition of recording and erasing is reduced, so that the recording characteristics are not degraded even if recording, erasing or rewriting is performed many times. It is to provide a small number of optical recording media.

Another object of the present invention is to provide a long-life optical recording medium which is excellent in oxidation resistance and moist heat resistance and has no defects even during long-term storage.

Still another object of the present invention is to provide an optical recording medium having high recording sensitivity and excellent recording characteristics such as a carrier-to-noise ratio and an erasing ratio.

Still another object of the present invention is to provide a method for manufacturing an optical recording medium having a high sputtering rate and excellent productivity.

[0013]

According to the present invention, information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
An optical recording medium performed by a phase change between an amorphous phase and a crystalline phase, wherein the optical recording medium has at least a recording layer, a dielectric layer, and a reflective layer, and the composition of the reflective layer is palladium, hafnium, and The present invention relates to an optical recording medium made of aluminum and having a composition represented by the following formula.

[0014] Formula _{Pd x Hf y Al 1-xy} 0.001 <x <0.01 0.005 <y <0.10 where x, y, 1-xy, the atomic ratio of each element (mole Ratio).

The present invention also relates to a method for manufacturing an optical recording medium, wherein a reflective layer is formed by sputtering an Al alloy target having a composition represented by the above formula.

Furthermore, the present invention relates to an Al alloy for a sputtering target for forming a reflective layer of an optical recording medium having a composition represented by the above formula.

The main component A of the reflective layer of the optical recording medium of the present invention is A
1 is effective for improving the contrast of a reproduced signal by utilizing optical interference with high light reflectance. Further, the thermal conductivity is high, the formation of amorphous recording marks is facilitated by the cooling effect, and the erasing characteristics can be improved by flattening the heat distribution during erasing. Also, Al
Is less expensive than precious metals such as gold, and can reduce manufacturing costs.

The additive element Pd (palladium) of the reflective layer of the present invention is added to Al to increase the recrystallization temperature of Al, improve the thermal stability of the crystalline state of the Al reflective layer, and improve the crystal grain size. Suppress coarsening of the diameter. This has the effect of reducing fluctuations and deterioration in recording characteristics and reproduction signal quality due to heating due to repeated recording and erasing.

Further, the additive element Hf of the reflection layer of the present invention is:
The oxidation resistance and wet heat resistance of Al are significantly improved, and the life of the optical recording medium can be extended.

The addition elements Pd and Hf of the present invention, when added to Al, slightly lower the thermal conductivity of the Al alloy in the reflective layer as compared with Al, and as a result, the recording and erasing sensitivity of the optical recording medium is reduced. And the recording mark is enlarged at the time of recording to improve the reproduction signal contrast and c /
There is also an effect of improving n.

Further, the Al alloy reflective layer of the present invention to which Pd and Hf are added has a high reflectance and is almost the same as pure Al. Therefore, wasteful light energy absorbed by the reflective layer is small, and the irradiated light energy is efficiently absorbed by the recording layer, so that a highly sensitive recording medium can be configured.

The amount of Pd and Hf contained in the reflective layer of the present invention
Since the amount is very small, the increase in the production cost due to the use of Hf and Pd is hardly a problem.

When the amount x of the additional element Pd in the reflective layer of the present invention is 0.001 or less, the above-mentioned significant addition effect is not exhibited, and when it is 0.01 or more, the compound phase of Pd and Al becomes Due to factors such as the presence of a large amount in the alloy, properties such as the mechanical strength, thermal stability of the crystalline state, and wet heat resistance of the alloy deteriorate.

When the amount y of the additional element Hf in the reflective layer of the present invention is 0.005 or less, the above-mentioned significant addition effect is not exhibited, and when the amount y is 0.10 or more, the metal compound phase of Hf and Al is used. Due to the presence of a large amount of in the alloy, the properties such as the mechanical strength of the alloy, the thermal stability of the crystalline state, and the resistance to moist heat are reduced, and the thermal conductivity of the reflective layer becomes too low, resulting in erasure. The characteristics and the number of repetitions that can be repeated are significantly reduced.

Since the effect of preventing a change in the crystal state of the Al alloy due to repetition of recording and erasing is high, the additive element P
the amount x of d is not less than 0.001 and not more than 0.005;
It is preferable that the addition amount y of f is 0.005 or more and 0.05 or less.

The constituent member of the optical recording medium according to the present invention is, for example, a structure in which light is incident from the substrate side and used.
A laminated structure of first dielectric layer / recording layer / second dielectric layer / reflective layer can be employed. However, the present invention is not limited to this, and a resin layer such as an ultraviolet curable resin, an adhesive layer for bonding to another substrate, or the like may be provided on the reflective layer as long as the effects of the present invention are not impaired.

The thickness of the reflective layer of the present invention is not particularly limited, but is usually 30 nm to 300 nm. In particular, the thickness is preferably 50 nm or more and 150 nm or less because the recording and erasing sensitivity is high and the erasing characteristics such as the erasing rate are excellent.

Although the recording layer of the present invention is not particularly limited, a Pd—Ge—Sb—Te alloy, Pt—G
e-Sb-Te alloy, Ni-Ge-Sb-Te alloy, G
e-Sb-Te alloy, Co-Ge-Sb-Te alloy, I
There are an n-Sb-Te alloy, an In-Se alloy, and the like.

Pd-Ge-Sb-Te alloy, Pt-Ge
-Sb-Te alloys and Ge-Sb-Te alloys are preferable because the erasing time is short and recording and erasing can be repeated many times. Particularly, Pd-Ge-Sb-Te alloys and Pt-Ge- Sb-Te alloys are preferred because of their excellent properties.

The thickness of the recording layer of the present invention is not particularly limited, but is 10 to 150 nm. In particular, the recording and erasing sensitivity is high, and the recording and erasing can be performed many times.

The dielectric layer according to the present invention is for preventing a substrate, a recording layer, and the like from being deformed by heat during recording and deteriorating recording characteristics. As this dielectric layer, Zn
There are inorganic thin films such as S and SiO ₂ . Particularly, a thin film of ZnS, a thin film of an oxide of a metal such as Si, Ge, Ti, Zr, and Te, and a film of a mixture thereof are preferable because of high heat resistance. Particularly, a mixed film of ZnS and SiO ₂ is used for recording,
It is preferable because deterioration of recording sensitivity, c / n, erasure rate, and the like hardly occurs even by repeating erasure. The thickness of the dielectric layer is approximately 10-500 nm. The dielectric layer
The thickness is preferably 10 to 400 nm because it is hard to peel off from the substrate or the recording layer and hardly causes defects such as cracks.

In particular, since one-beam overwriting can be performed at high speed, the erasing rate is large, and the erasing characteristics are good, it is preferable to constitute the main part of the optical recording medium as follows.

That is, the thickness of the first dielectric layer is set to 100
and the thickness of the second dielectric layer is 10 nm to 400 nm.
nm to 30 nm, and the thickness of the recording layer is 10 nm to
The structure is such that the recording layer is quenched during recording and erasing operations, the dielectric layer is a mixed film of ZnS and SiO ₂ , and the composition of the recording layer is as follows. It is preferable to be within the range represented by the formula.

[0034] _{(M x Sb y Te 1-} xy) 1-z (Te 0.5 Ge 0.5) z 0.0005 ≦ x ≦ 0.01 0.35 ≦ y ≦ 0.65 0.2 ≦ z ≦ 0.5 However, x, y, z, and 0.5 represent the atomic ratio of each element.

M represents at least one element of Pd and Pt.

The substrate of the present invention may be the same as that of a conventional recording medium, such as plastic, glass, or aluminum. When recording is performed from the substrate side using a focused light beam for the purpose of avoiding the influence of dust, scratches on the substrate, and the like, it is preferable to use a transparent material for the substrate. Examples of such a material include glass, polycarbonate, polymethyl methacrylate, polyolefin resin, epoxy resin, and polyimide resin.

In particular, polycarbonate resin and epoxy resin are preferable because of their low optical birefringence, low hygroscopicity and easy molding. Particularly when heat resistance is required, epoxy resin is preferred.

The thickness of the substrate is not particularly limited, but is practically 0.01 mm to 5 mm. 0.01m
If it is less than m, even when recording with a light beam focused from the substrate side, it is susceptible to dust, and if it is 5 mm or more,
This is because it becomes difficult to increase the numerical aperture of the objective lens and the spot size of the irradiation light beam becomes large, so that it becomes difficult to increase the recording density. The substrate may be flexible or rigid. Flexible substrates are tape, sheet,
Use in card form. The rigid substrate is used in the form of a card or a disk. Also, these substrates
After forming the recording layer and the like, an air sandwich structure, an air incident structure, and a close bonding structure may be used by using two substrates.

The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as a laser beam or a strobe light. In particular, a semiconductor laser beam has a small light source, low power consumption, Is preferred because of the simplicity.

Recording is performed by irradiating a laser beam pulse or the like to the crystalline recording layer to form an amorphous recording mark. Alternatively, a recording mark in a crystalline state may be formed on a recording layer in an amorphous state. Erasing can be performed by irradiating a laser beam to crystallize an amorphous recording mark or to make a crystalline recording mark amorphous.

Since the recording speed can be increased and the recording layer is hardly deformed, it is preferable to form an amorphous recording mark at the time of recording and crystallize at the time of erasing.

When forming a recording mark, the light intensity is high.
One-beam overwriting, in which erasing is slightly weakened and rewriting is performed by one light beam irradiation, is preferable because the time required for rewriting is reduced.

Next, a method for manufacturing the optical recording medium of the present invention will be described. Examples of a method for forming a reflective layer, a recording layer, and the like on a substrate include a known thin film forming method in a vacuum, for example, a vacuum deposition method, an ion plating method, and a sputtering method. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled.

The Al alloy constituting the reflective layer of the present invention has a higher sputtering rate and higher productivity than conventional pure Al or an alloy obtained by adding a small amount of Ti to Al.
The reflective layer is preferably formed by a sputtering method using an Al alloy having the composition of the reflective layer of the present invention as a target. In this case, the alloy used as the target has a composition represented by the following formula.

The formula _{Pd x Hf y Al 1-xy} 0.001 <x <0.01 0.005 <y <0.10 where x, y, 1-xy, the atomic ratio of each element (mole Ratio).

The thickness of the reflective layer and the recording layer to be formed can be easily controlled by monitoring the state of deposition using a known technique such as a quartz oscillator film thickness meter.

The formation of the reflection layer, the recording layer, and the like may be performed while the substrate is fixed, or may be moved or rotated. The substrate is preferably rotated on its own because of excellent in-plane uniformity of the film thickness, and more preferably combined with revolution.

In addition, as long as the effects of the present invention are not significantly impaired, scratches, scratches,
In order to prevent deformation and the like, a resin protective layer such as a known ultraviolet curable resin may be provided as necessary. Further, after forming the recording layer, the dielectric layer, or the like, or further forming the above-mentioned resin protective layer, the two substrates may be opposed to each other and bonded with a known adhesive.

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (Analysis and Measurement Method) The compositions of the reflective layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Instruments Inc.).
The carrier-to-noise ratio and the erasing rate (difference in the reproduced carrier signal strength after recording and after erasing) were measured by a spectrum analyzer.

The thicknesses of the recording layer, the dielectric layer, and the reflection layer were monitored by a quartz oscillator thickness meter. The film thickness of the reflective layer and the like was measured by observing the cross section with a scanning or transmission electron microscope after the layer was formed.

Example 1 I having a thickness of 1.2 mm, a diameter of 13 cm, and a pitch of 1.6 μm
A recording layer, a dielectric layer, and a reflective layer were formed by a high-frequency sputtering method while rotating an SO-compliant preformat and a polycarbonate substrate with a spiral groove at 30 revolutions per minute.

First, the inside of the vacuum vessel was evacuated to 1 × 10 ^-5 Pa, and then SiO 2 was evacuated in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
₂ was sputtered ZnS added 20 mol%, to form a dielectric layer having a film thickness of 370nm on the substrate. Then, P
An alloy target composed of d, Ge, Sb, and Te was sputtered to form a recording layer having a composition of Pd ₁ Ge ₁₇ Sb ₂₆ Te ₅₆ (atomic%) with a thickness of 20 nm. Further, the above-described dielectric layer was formed to a thickness of 20 nm, and was sputtered thereon using an Al target on which small pieces of Pd and Hf were arranged to form Pd _0.002
A reflective layer of Hf _0.02 Al _0.978 alloy having a thickness of 100 nm was formed. Further, after taking out the disk from the vacuum chamber, an acrylic UV curable resin was spin-coated on the reflective layer, and cured by irradiation with ultraviolet light to form a resin layer having a thickness of 10 μm, thereby obtaining the optical recording medium of the present invention. .

This optical recording medium is rotated at a linear velocity of 5.5 m / sec, and irradiated with a semiconductor laser beam having a wavelength of 820 nm condensed from the substrate side into an ellipse of 22 × 66 μm under the condition of a film surface intensity of 1.1 W. Thus, the recording layer was crystallized and initialized.

Thereafter, at a position of a radius of 30 mm, the number of rotations is 1
Under the conditions of 800 rpm, using an optical head having a numerical aperture of the objective lens of 0.5 and a semiconductor laser wavelength of 830 nm, a frequency of 3.7 MHz (corresponding to 1.5T of 2-7 code), a pulse width of 50 nsec, and a peak power of 19 mW. ,
A semiconductor laser beam modulated to a bottom power of 9 mW was irradiated on one track to form an amorphous mark and recorded. When this track was reproduced by irradiating a semiconductor laser beam having a reproduction power of 1.3 mW, under the condition of a bandwidth of 30 kHz,
A good c / n ratio of 53 dB, a value sufficient for digital recording was obtained, and almost no defects were observed.

Further, this portion was irradiated with a semiconductor laser beam modulated at 1.4 MHz (corresponding to 4.0T of 2-7 code) in the same manner as above, and one-beam overwriting was performed. When this part was reproduced again, the 3.7 MHz recording was 1.
It was completely rewritten to 4 MHz. 3.7MH at this time
When the erase ratio of z was measured, the erase ratio was 30 dB.
A value well above the required about 20 dB was obtained. Further, the same measurement was performed after the repetition of the one-beam overwriting with a signal of 3.7 MHz was repeated 1000 times and 200,000 times, but the changes in c / n and erasure rate were 2
Deterioration was hardly recognized within dB, and almost no increase in recording defects was observed.

After the optical recording medium was placed in an environment of 80 ° C. and a relative humidity of 80% for 2000 hours, the recorded portion was reproduced. However, the change in the c / n ratio was less than 2 dB and hardly changed. Further, recording and erasing were performed again, and the c / n ratio and the erasing rate were measured. As a result, similarly, there was almost no change and almost no increase in defects was observed. From this result, it can be estimated that this disk has a media life of 10 years or more.

Example 2 Each of the reflection layers of Example 1 was made of Pd _0.001 Hf _0.03 Al
Optical recording media having the same configuration as in Example 1 _{except that a 0.969} alloy, a Pd _0.003 Hf _0.01 Al _0.987 alloy, and a film having a thickness of 100 nm were produced. When recording, rewriting, and reproducing were performed on this optical recording medium in the same manner as in Example 1, the change in c / n and erasure rate was less than 2 dB compared to the 100th repetition even after 200,000 repetitions of rewriting. Not possible, c / n 52d
B, a good value of an erasing rate of 30 dB was obtained, and there was almost no occurrence of defects in the recording portion.

COMPARATIVE EXAMPLE 1 The reflective layer of Example 1 was made of Al having a purity of 99.99% and a film thickness of 70%.
An optical recording medium having the same configuration as that of the example 1 except that the film thickness was set to be nm was manufactured. When this optical recording medium was recorded and rewritten 100,000 times under the same conditions as in Example 1, the number of defective portions increased.

After the optical recording medium was placed in an environment of 80 ° C. and a relative humidity of 80% for 2000 hours, when the recorded portion was reproduced, a decrease in the reflectance and a remarkable increase in defects were observed.

COMPARATIVE EXAMPLE 2 The reflective layer of Example 1 was formed with an Al film having a purity of 99.99% and a thickness of 10%.
An optical recording medium having the same configuration as in Example 1 except that the film was formed to a thickness of 0 nm was manufactured. When recording and rewriting were attempted under the same recording power conditions as in Example 1, the recording sensitivity was low and recording was difficult.

Example 3 The sputtering target for the reflective layer in Example 1 was composed of Pd.
An optical recording medium having a similar configuration was manufactured under the same manufacturing conditions as in Example 1 _{except that} an alloy target of _0.002 Hf _0.02 Al _0.978 was used. When recording, rewriting, and reproducing were performed on this optical recording medium in the same manner as in Example 1, the change in c / n and erasure rate was 2 compared to the 100th time even after 200,000 repetitions of rewriting.
When it was less than dB, it was hardly observed, and good values of c / n 52 dB and erasure rate 30 dB were obtained, and there was almost no occurrence of defects in the recording portion.

Example 4 Only the reflection layer was formed by the same planar magnetron high-frequency sputtering method as in Example 1, and the formation speed of the reflection layer was measured.

First, the inside of the vacuum vessel was evacuated to 1 × 10 ^-5 Pa, and then revolved at a rate of 30 revolutions per minute in an Ar gas atmosphere of 2 × 10 ^-1 Pa on a 1.1 mm thick glass plate. To
A reflective layer was formed. Example 3 for the sputter target
A composition P in the form of a disk having a diameter of 5 inches and a thickness of 6 mm similar to
A sintered material target of d _0.002 Hf _0.02 Al _0.978 alloy was used. The sputtering power is a high frequency input (traveling wave) 60
0 W and a reflected wave of 40 W. Sputtering was performed under these conditions for 253 seconds to form a reflective layer. After taking out from the vacuum vessel, the thickness of the reflective layer was determined to be 100 nm. Therefore, the formation rate of the reflective layer under this condition is 0.395 n
m / sec.

COMPARATIVE EXAMPLE 3 The same size Ti was used as the sputter target of Example 4.
A reflection layer of a conventional Ti-added Al alloy was formed in the same manner as in Example 4 _{except that} a sintered material target of _0.03 Al _0.97 alloy was used, and the formation speed of the reflection layer was measured. The sputtering power was the same as that of Example 4 with a high-frequency input (traveling wave) of 600 W and a reflected wave of 40 W. The formation speed of this reflective layer is 0.1.
244 nm / sec, which is 38% slower than Example 4.
Productivity was poor.

[0065]

According to the present invention, since the configuration of the optical recording medium is a configuration having a reflective layer of a specific material, the following effects are obtained. (1) Even if recording and erasing are repeated a number of times, the operation is stable, and there is almost no deterioration in characteristics and no generation of defects. (2) It has excellent heat and moisture resistance and oxidation resistance, and has a long service life. (3) High erasure rate, high c / n, and high sensitivity. (4) It can be manufactured with high productivity by the sputtering method. (5) It can be a low-cost optical recording medium.

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Claims (3)

(57) [Claims] 1. A recording layer formed on a substrate is irradiated with light so that information can be recorded, erased, and reproduced, and the information can be recorded and erased in a phase between an amorphous phase and a crystalline phase. An optical recording medium performed by change, wherein the optical recording medium has at least a recording layer, a dielectric layer, and a reflective layer, and the composition of the reflective layer is composed of palladium, hafnium, and aluminum, and the composition is represented by the following formula: An optical recording medium represented by Formula _{Pd x Hf y Al 1-xy} 0.001 <x <0.01 0.005 <y <0.10 where x, y, 1-xy, the atomic ratio of each element (molar ratio) It represents. 2. A method for manufacturing an optical recording medium, comprising forming a reflective layer by sputtering an Al alloy target having a composition represented by the following formula. Formula _{Pd x Hf y Al 1-xy} 0.001 <x <0.01 0.005 <y <0.10 where x, y, 1-xy, the atomic ratio of each element (molar ratio) It represents. 3. An Al alloy for a sputtering target for forming a reflective layer of an optical recording medium having a composition represented by the following formula. Formula _{Pd x Hf y Al 1-xy} 0.001 <x <0.01 0.005 <y <0.10 where x, y, 1-xy, the atomic ratio of each element (molar ratio) It represents.