JP2001167477A - Phase change type optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase change type optical disk having enhanced recording and reproduction characteristics by improving the state of the surface of a reflection layer film-formed on a substrate. SOLUTION: The phase change type optical disk 10 having at least a reflection layer 2, a first protective layer 3, a phase change type recording layer 4, a second protective layer 5, an adhesive layer 6 and a second substrate 7 which are laminated in this order on a first substrate having a guide groove formed thereon is characterized in that the reflection layer 2 is constituted of two or more metal layers (1st to nth) consisting of the same material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk capable of optically recording and reproducing information.

[0002]

2. Description of the Related Art As a conventional phase-change type optical disk 20, a first substrate 1 having a guide groove as shown in FIG.
It is generally known that a first protective layer 12, a phase-change recording layer 13, a second protective layer 14, and a reflective layer 15 are provided in this order on the first layer 1 and a protective film 16 is formed on the reflective layer 15. ing.
Note that reference numeral 17 denotes an adhesive layer, and reference numeral 18 denotes a second substrate. The laser light is incident from the first substrate 11 surface side. Such an optical disc 20 is, for example, a DVD-RAM or a D-RAM using an optical system having an objective lens with an aperture ratio (NA) of 0.6.
Known as VD-RW.

Recently, in order to further increase the recording capacity, a system using a shorter recording wavelength and a higher NA objective lens has been proposed. For example, for recording and reproduction, a wavelength of 400 nm
Using a nearby semiconductor laser and an optical system with NA of 0.85, a capacity of 20 GB or more has been demonstrated.
However, when the NA is increased, it is necessary to reduce the thickness of the substrate on the light beam incident side in order to suppress aberration due to the thickness of the transmitting substrate. However, forming a guide groove or forming a recording medium on a thin substrate is difficult to manufacture and increases the warpage of the substrate.

For this reason, as shown in FIG. 4, a laminated film comprising a reflective layer 2, a recording layer 4, and protective layers 3 and 5 is sequentially provided on a first substrate 1 having a relatively large thickness. It is known that a second substrate 7 having a small thickness is bonded via an adhesive layer 6 to form a phase-change optical disk 10. Alternatively, Japanese Patent Application Laid-Open No. 9-63120 describes that a transparent layer is formed on the surface of a laminated film.

[0005]

The substrate surface 11
In the conventional forward-stacking type optical disc 20 that performs recording and reproduction by irradiating a laser beam from the side, the influence of the crystal grain boundary of the reflective layer 15 could be almost ignored. That is, since the reflective layer is deposited from the laser light incident surface side and nucleation is minutely generated, the interface of the reflective layer 15 can form a smooth surface. However, in the large-capacity optical disk 10 using an optical system with a high NA, the reflection layer 2 on the opposite side to the conventional optical disk 20 is used.
Since the recording and reproduction light is irradiated from the surface side of the light-emitting device and the return light from the reflective layer 2 is detected, the flatness of the surface of the reflective layer 2 greatly affects the signal quality. It is currently reflective layer 2
Al and Al alloy thin films widely used as
This is because columnar crystals are easily generated and the surface of the reflective layer 2 is roughened due to this.

The process of forming this surface is considered as follows. A pair of atoms formed by collision of a thin film atom with the substrate becomes a nucleus, and nucleation occurs. At the beginning of the thin film formation, the structure of the thin film is an island shape. Then, the size of the island increases, and the crystal grows with a preferred orientation. When the island becomes large and the adjacent islands come into contact, the lateral growth of the island is completed and the vertical growth starts.

Then, as the thin film is deposited on the substrate, sputtered particles flying from random directions cannot enter between the columnar crystals, voids are generated between the columnar crystals by the shadowing effect, and This is because tapering occurs and a large surface with unevenness of 5 to 10 nm is formed. The crystal grain size may be 100 nm or more, and voids are generated at the crystal grain boundaries, so that the orientation of the particles is poor and light scattering on the surface of the film is large, so that a large noise is generated. . For example, for a 3T signal (0.4 μm in length, 0.3 μm in width, and 65 nm in pit depth), which is the shortest mark of a DVD, the size is not negligible.

In the case of using a blue semiconductor laser with a shorter wavelength, the size of the recording mark, emboss pit, or guide groove for recording / reproducing light becomes smaller. In some cases, the pattern is buried and the reproduced signal cannot be extracted.

Further, since the laminated film is formed in the reverse order to the conventional optical disc 20 of the type laminated in the forward direction,
The form of the reflective layer 2 formed first is reflected on the protective layers 3 and 5 and the recording layer 4 provided thereafter, and a laminated film with impaired flatness is formed. Therefore, compared to the conventional optical disc 20, the noise is higher and the jitter is higher. Accordingly, the number of times of rewriting also decreases.

For example, in forming the reflective layer 2, Japanese Patent Application Laid-Open No. 9-63120 uses an ion beam sputtering method. Unlike the DC magnetron sputtering used in the production of DVDs and CDs, this film formation method requires the introduction of a new apparatus, which increases the production cost.
It is technically difficult to incorporate a direct current (DC) magnetron sputter for forming a recording layer, an alternating current (RF) sputter for forming a protective film, and an ion beam sputter into an integrated film forming apparatus.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. As a first invention, at least a reflective layer 2 and a first layer 1 are provided on a first substrate 1 in which a guide groove is formed.
A phase-change optical disk 10 in which a protective layer 3, a phase-change recording layer 4, a second protective layer 5, an adhesive layer 6, and a second substrate 7 are laminated in this order, and the reflective layer 2 is made of the same material. The phase change type optical disk 10 composed of two or more metal layers (first to n-th) is referred to as a second invention, and the crystal grain size of the metal forming one reflection layer 21 is reduced to the other reflection layer. The phase change type optical disk according to claim 1, which is smaller than the particle diameter of the metal constituting the second layer, wherein one of the reflective layers is close to the first substrate. A phase change optical disk 10 is provided.

[0012]

FIG. 1 is a sectional view showing an embodiment of a phase change type optical disk 10 according to the present invention. In the drawing, reference numeral 1 denotes a first substrate on which a pre-groove for guiding a laser beam, a pre-pit or a non-rewritable reproduction signal is provided by an emboss pit. The material of the substrate 1 is polycarbonate,
A plastic substrate such as polyolefin or acrylic or a glass substrate is used. Further, since laser light does not enter through the first substrate, a metal plate having no light-transmitting property, such as an aluminum plate, can be used. The pre-grooves and pre-pits for guiding the laser beam are directly injection-molded, or a polymer is cured by dropping a photopolymer on a stamper and placing a smooth first substrate on the photopolymer.
It is formed by a method (photopolymer method).

Also, CAV (constant angular velocit)
y Constant angular velocity, CLV (constant linear velocity constant linear velocity) or ZCAV (zone constant angular)
velocity) and ZCLV (zone constant linear veloci)
ty), and an address signal may be recorded in advance as an emboss pit at the head of each sector. The information area used by the user is formed of a vacant groove and wobbled as needed. Groove recording, land recording, or land-groove recording method is selected. When recording is performed on the land and the groove, the width of the land and the groove are determined so that the reproduced signals of the land and the groove become equal to each other. The track pitch is 0.1 to 1.6 μm and the groove depth is 10 to 200 nm
Is preferred.

The first substrate 1 is set in a vacuum film forming apparatus, and the first reflection layer 21, the second or more reflection layers 22, 23, the first protection layer 3, the phase change recording layer 4, and the second protection layer are provided. 5 are sequentially formed. As a film forming method, resistance heating type or electron beam type vacuum evaporation, direct current or alternating current sputtering, reactive sputtering, ion beam sputtering, ion plating and the like are used.

The reflection layer 2 is composed of two or more reflection layers made of the same material. For example, it is composed of a first reflective layer 21, a second reflective layer 22, and an n-th (n is 3 or more) reflective layer 23. First, the film formation rate of the first reflective layer 21 is set to the second
The film forming speed of the reflective layers 22 and 23 is set to be lower than the film forming speed. By doing so, the surface roughness (particle size) of the metal of the first reflective layer 21 is minimized, and the particle size of the second or more reflective layers 22 and 23 deposited thereon is larger than that of the first reflective layer 21. However, the surface property is reduced as compared with the case where no division is performed, and the surface property becomes smooth. Fig. 2 shows the distribution of crystal grain size. As is clear from FIG. 2, the carrier level at the time of reproduction increases and noise decreases. Further, an increase in jitter due to rewriting is suppressed, and the number of times of rewriting is increased.

A reflection layer (first reflection layer) 2 on the first substrate 1 side
The reason why the surface roughness of the first reflective layer 21 is reduced when 1 is deposited at a low deposition rate is considered as follows. When deposited at a low deposition rate, the number of nuclei generated on the substrate increases, so the size of islands in the initial stage of thin film formation decreases,
The diameter (particle size) of the columnar crystal becomes thin. That is, the orientation of the particles is improved. Further, since the sputtered particles enter between the islands, the occurrence of voids is reduced and the taper is also reduced. Also, splitting the sputtering process
This also has the effect of preventing crystal growth from continuing. In this way, the crystal grain size is reduced and a dense and flat thin film is formed, so that light scattering is reduced.

The reflection layer 2 is made of Al, Au, Ag, Cu, N
Metals or semiconductors such as i, In, Ti, Cr, Pt, and Si, and alloys and semiconductors thereof are used. It is preferable to add a metal or a semiconductor, rather than a simple metal, because the crystal grains become smaller. Further, in order to improve the stability under high temperature and high humidity, it is better to include an additive. For example,
Al-Ti, Al-Cr, Al-Zr, Al-Si, A
Alloys such as g-Pd-Cu can be used. 400 nm wavelength
When using a blue semiconductor laser, Al-based or Ag
Higher reflectance can be obtained by using a system alloy.

The first reflective layer 21 has a thickness of 5 to 100 nm,
The thickness of the second or more reflective layer 22 is preferably 30 to 200 nm. The reflective layer 2 is formed by, for example, using one cathode and sequentially laminating the first reflective layer 21 and the second or more reflective layers 22 and 23 in the same vacuum chamber, or using two or more cathodes to form separate vacuum layers. A first reflective layer and a second or more reflective layer 2 in a tank
2 and 23 are sequentially laminated.

When a reflecting layer 2 having a total thickness of 150 nm is formed by using a single-wafer sputtering apparatus in which substrates are transported one by one and each layer is formed in a plurality of vacuum chambers, the first vacuum chamber is used. When the first reflective layer 21 is formed at a film forming rate of 2 nm / s and the second and third reflective layers are formed at a film forming rate of 6.5 nm / s in the second and third vacuum chambers, Disks can be formed one after another in a short time of seconds. First reflective layer 21
In order to reduce the film forming speed, the time required for forming the entire laminated film can be reduced by forming the second reflective layer 22 or higher at a higher speed than the first reflective layer 21. If the reflection layer 2 is divided into three or more, the film formation time can be further reduced.

The first protective layer 3 and the second protective layer 5 are made of a metal oxide, nitride, sulfide or a mixture thereof. For example, ZnS-SiO2, ZnS, SiO2, T
a2O5, Si3N4, AlN, Al2O3, AlSiON,
A simple substance such as ZrO2 or TiO2 or a mixture thereof is used.

The first protective layer 3 is thinner than the second protective layer 5, has a so-called quenching structure, and preferably has a thickness of 2 to 50 nm in order to reduce thermal damage. Preferably, the deposition rate of the first protective layer 3 is lower than the deposition rate of the second protective layer 5. This suppresses an increase in jitter due to rewriting and increases the number of rewriting.

Reference numeral 4 denotes a phase change type recording layer made of a phase change material utilizing a change in reflectivity between amorphous and crystal or a change in phase. Ge-Sb-Te system, Ag-In-Te
An alloy containing Te or Sb as a main component, such as -Sb-based or Cu-Al-Sb-Te-based, may be used. The thickness of the phase-change recording layer 4 is 10 to 100 nm, preferably 10 to 100 nm in order to increase the recording sensitivity and increase the reproduction signal.
The thickness is preferably 30 nm. Further, although not shown, on one or both sides of the phase change recording layer 4, a crystallization promoting layer for improving the erasing rate, an impurity diffusion suppressing layer for reducing aging and improving rewriting performance, An adhesion reinforcing layer may be provided.

Reference numeral 5 denotes a second protective layer made of the same material as the first protective layer 3. The thickness of the second protective layer 5 is 10 to 200 n.
m. The optimum film thickness varies depending on the wavelength of the light source used, but is preferably set to 40 to 150 nm in order to increase the reproduction signal. When the recording laser light is blue (wavelength about 400 nm), 40 to 60 n
When m is set, a large modulation degree can be obtained.

The adhesive layer 6 is formed by taking out the formed disk into the atmosphere and applying an ultraviolet curable resin on the second protective layer 5. The film thickness is between 1 and 200 microns. As a coating method, a spin coating method, a spray method, a dipping method, a blade coating method, a roll coating method, a screen printing method, or the like is used. The ultraviolet curable resin as the adhesive layer 6 comprises at least a prepolymer, a monofunctional acrylate monomer, a polyfunctional acrylate monomer and the like, and a photopolymerization initiator. The adhesive layer 6 is transparent without absorption for the wavelength of the recording / reproducing light. When a time is required from the film formation to the bonding of the second substrate 7 or when the substrate needs to be transported in the process, a protective film made of an ultraviolet curable resin is preferably provided in a thickness of 1 to 20 μm.

Reference numeral 7 denotes a second substrate, which is made of a light-transmitting plastic substrate such as polycarbonate, polyolefin, or acrylic, or a glass substrate. The thickness of the second substrate 7 is 0.01 mm to 1.2 mm. When the NA is large, the substrate thickness is reduced to suppress the influence of spherical aberration. If necessary, a hard coat or an antistatic agent may be provided on the second substrate 7. A medium can be used in a cartridge in order to improve the mounting property to the recording apparatus and the protection property in handling.

The optical disk 10 thus manufactured is irradiated with a laser beam, a flash lamp, or the like to heat the phase-change recording layer 4 to a temperature higher than the crystallization temperature, thereby performing an initialization process. Practically, the laser beam applied to the optical disk 10 has a beam diameter larger than the track width, and is preferably longer in the radial direction, and simultaneously initializes a plurality of tracks while rotating the disk.

[0027]

Example 1 Track pitch 0.74 μm, groove depth 30
The first reflection layer 21 is formed on a polycarbonate substrate (first substrate) 1 having a thickness of 0.6 mm provided with a pre-groove (groove width 0.3 μm, land width 0.44 μm) of nm.
The second reflective layer 22, the first protective layer 3, the phase change recording layer 4, the second
The protective layer 5 was sequentially formed by sputtering to form a laminated film. Specifically, after evacuating to a degree of vacuum of 1 × 10 −6 Torr or less, an Ar gas was flown to form a laminated film in an atmosphere of 2 mTorr. In forming the laminated film, first, the reflective layer 2 was divided into two and formed to have a total thickness of 150 nm. First, Al (9
(9.99%) by DC (direct current) sputtering to provide a first reflective layer 21 having a thickness of 20 nm. The deposition rate is 0.1 nm
/ S at a low speed.

Next, once the power of the DC power supply is turned off, the power is turned on again, and the second reflective layer 22 is formed with the same target at a deposition rate of 0.6 nm / s, which is six times that of the first reflective layer, at 130 nm / 130 nm. Provided. ZnS-SiO2 (80:
RF (high frequency) sputtering to provide 17 nm as the first protective layer 3. The deposition rate is 0.08
nm / s. Next, Ag4 was used as the phase-change recording layer 4.
(At%) In4 (at%) Sb63 (at%) Te29 (at
%) Was formed to a thickness of 20 nm by a DC sputtering method. On this, ZnS-SiO2 (80:20) is formed as a second protective layer 5.
mol%) by RF sputtering. The deposition rate is 0.2 nm / s.

After taking out the disk from the vacuum chamber, an ultraviolet curable resin (X, manufactured by Sumitomo Chemical Co., Ltd.) is used as the adhesive layer 6.
R98) is spin-coated on the second protective layer 5, and a polycarbonate substrate (second substrate) 7 having a thickness of 0.6 mm is put on the substrate in an uncured state and bonded together. To cure the adhesive layer 6 to obtain the optical disc 10. The thickness of the adhesive layer 6 was 8 μm.

Next, the recording / reproducing characteristics of the optical disk 10 were examined. First, the optical disk 10 was rotated and irradiated with laser light from the second substrate 7 side to initialize the phase change recording layer 4 by changing its phase from an amorphous state to a crystalline state having a high reflectance. Recording was performed on the groove portion of the phase change recording layer 4 from the substrate 7 side. The groove has a convex shape when viewed from the incident direction of the laser beam.

The recording condition is that the recording laser wavelength is 635 n
m, the NA of the objective lens was 0.6, and the modulation signal, recording strategy and the like conformed to BOOK ver. 0.9 of DVD-RW. Peak power 15.0 mW, bias power 7.5
mW. Recording was performed by modulating a laser beam with a bottom power of 0.5 mW, and reproduction was performed with a reproduction light of 0.7 mW. Standard deviation σ
Was divided by the window width Tw, and the carrier and noise level of the 3T signal as the shortest mark were measured. The initial jitter increased by 9.1%, and the jitter after 1000 direct overwrites increased by 2.5%. The initial carrier level was 23.4 dBm, and the initial noise level was 71.5 dBm. The optical disk 20 manufactured under these conditions exhibited low noise and a sufficiently low jitter even after many rewrites, and showed signal quality equivalent to that of the conventional optical disk 20.

[0032]

Example 2 As in Example 1, the reflective layer 2 was formed by dividing it into two parts. 100 nm was provided as the first reflection layer 21. The deposition rate was as low as 0.1 nm / s. Next, the second reflective layer 22 was formed at a deposition rate of 0.6 nm / 0.6 times that of the first reflective layer 21.
s was set to 50 nm. Except for this, an optical disk 10 was manufactured in the same manner as in Example 1, and the recording / reproducing characteristics were examined. Initial jitter is 10.2%, direct overwrite 10
The jitter after 00 times increased by 1.8%. The initial carrier level is 23.9 dBm and the initial noise level is 70.
It was 5 dBm. Optical disk 10 manufactured under these conditions
Showed low noise and sufficiently low jitter even after many rewrites, and signal quality equivalent to that of the conventional optical disc 20.

[0033]

[Embodiment 3] With the same material composition as in Embodiment 1, only the reflection layer 2 was formed by dividing it into three parts. The first reflective layer 21 was provided with a thickness of 50 nm at a low deposition rate of 0.1 nm / s. Next, the second
The reflection layer 22 is formed at a low deposition rate of 0.2 nm / s at a rate of 50 nm.
nm. Further, as the third reflective layer 23, 50 nm was provided at a high film forming rate of 0.6 nm / s. Except for this, an optical disk 10 was manufactured in the same manner as in Example 1, and the recording / reproducing characteristics were examined. The initial jitter increased by 10.0%, and the jitter after 1000 direct overwrites increased by 1.6%.
The initial carrier level was 23.7 dBm and the initial noise level was 70.3 dBm. The optical disc 10 manufactured under these conditions has low noise and shows a sufficiently low jitter even after many rewrites, and shows signal quality equivalent to that of the conventional optical disc 20.

As described above, as is apparent from Examples 1 to 3, by setting the film forming speed of the first reflective layer 21 to be lower than that of the second reflective layer 21, the surface roughness of the first reflective layer 21 ( Since the particle diameter is smaller than that of the second particle, the orientation of the particles is improved, and the scattering of light on the surface is reduced, so that the number of carriers during reproduction is increased and noise is reduced. Further, an increase in jitter due to rewriting is suppressed, and the number of times of rewriting is increased.

[0035]

Comparative Example 1 The reflection layer 2 was formed without being divided. A 150 nm film was formed at a film forming speed of 0.6 nm / s. Except for this, an optical disk 20 was produced in the same manner as in Example 1, and the recording / reproducing characteristics were examined. The initial jitter increased by 16.7%, and the jitter after 1000 direct overwrites increased by 5.0%.
The initial carrier level was 24.8 dBm, and the initial noise level was 60.5 dBm. The optical disk 10 manufactured under these conditions has high noise from the initial state,
The signal quality was inferior to that of the optical disk formed in the forward direction, exceeding the jitter value of 15% at which the system failed.

[0036]

Comparative Example 2 As in Example 1, the reflection layer was formed in two parts. The first reflective layer 21 was provided with a thickness of 60 nm. The film formation speed was as high as 0.6 nm / s. Next, the second reflection layer 2
2 is 1/6 of the first reflective layer and has a low deposition rate of 0.1 nm /
90 nm. Except for this, an optical disk 10 was manufactured in the same manner as in Example 1, and the recording / reproducing characteristics were examined. Initial jitter is 23.3%, direct overwrite 10
Jitter after 00 times could not be measured. The initial carrier level is 23.3 dBm and the initial noise level is 59.
It was 5 dBm. Optical disk 10 manufactured under these conditions
Was higher in noise from the initial state, and had a jitter value of more than 15% at which the DVD system failed, and the signal quality was inferior to that of the optical disc 20 formed in the forward direction.

As described above, according to the structures of Comparative Example 1 and Comparative Example 2, the structure in which the reflective layer 2 is not divided, and even if the reflective layer 2 is divided, the film forming speed of the first reflective layer 21 is reduced by the structure of the second reflective layer 22. Since the speed is set faster than the film speed, the surface roughness of the first reflective layer 21 increases, and therefore, the number of carriers during reproduction decreases and noise increases. Furthermore, the jitter due to rewriting increases,
This reduces the number of rewrites.

[0038]

According to the present invention, at least a reflective layer, a first protective layer, a phase-change recording layer, a second protective layer, an adhesive layer, and a second substrate are formed on a first substrate on which a guide groove is formed. A phase-change type optical disc laminated in order, wherein the reflection layer is composed of two or more metal layers made of the same material, whereby the same jitter and rewrite frequency as those of a conventional optical disc can be obtained, Since it is only necessary to divide the layer into two or more layers, it can be easily realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a phase-change optical disc according to the present invention.

FIG. 2 is a cross-sectional view showing a distribution of a crystal grain size of a reflection layer.

FIG. 3 is a cross-sectional view showing one embodiment of a conventional phase change optical disk.

FIG. 4 is a cross-sectional view showing another embodiment of a conventional phase change optical disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 reflective layer 3 1st protective layer 4 phase change type recording layer 5 2nd protective layer 6 adhesive layer 7 2nd substrate 10 phase change type optical disk 21 1st reflective layer 22 2nd reflective layer

Claims (3)

[Claims] 1. A phase in which at least a reflective layer, a first protective layer, a phase-change recording layer, a second protective layer, an adhesive layer, and a second substrate are laminated in this order on a first substrate on which a guide groove is formed. A changeable optical disc, wherein the reflection layer is made of the same material.
A phase-change type optical disc comprising at least a metal layer. 2. The phase-change optical disk according to claim 1, wherein the crystal grain size of the metal constituting one of the reflection layers is smaller than the grain size of the metal constituting the other reflection layer. 3. The phase change optical disk according to claim 2, wherein one of the reflection layers is close to the first substrate.