JP3365463B2 - Optical information recording medium and recording method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable and erasable optical information recording medium utilizing a reflectance difference or a reflected light phase difference caused by a phase change caused by laser light irradiation.
In particular, the present invention relates to an optical information recording medium having excellent rewriting characteristics.

[0002]

2. Description of the Related Art Optical discs include a read-only type, an optical recordable type, and a rewritable type. The read-only type is a video disc,
It has already been put to practical use as an audio disc and a disc memory for large-capacity computers. Typical examples of the optical recordable type are a drilling / deformable type, a magneto-optical type, and a phase change type.

A recording layer made of a low melting point metal such as Te or a dye is used as the perforation / deformation type and is locally heated by laser light irradiation to form a hole or a recess.
The magneto-optical type performs recording and erasing depending on the magnetization direction of the recording layer, and reproduces by the magneto-optical effect. As a disc for recording a CD format signal, an optical disc having a recording layer made of a dye or a polymer containing a dye on a substrate, and an optical information recording method using the optical disc have been proposed (Japanese Patent Laid-Open No. 61-237239). Issue 6,
No. 1-233943).

On the other hand, the phase change type utilizes the fact that the reflectance or the phase of the reflected light changes before and after the phase change.
Playback is performed by detecting the difference in the amount of reflected light without the need for an external magnetic field. Compared to the magneto-optical type, the phase-change type is easy to manufacture a drive because it does not require a magnet and has a simple optical system, and is advantageous in downsizing and cost reduction.

Further, there is an advantage that recording / erasing can be performed only by modulating the power of the laser beam, and one-beam overwriting in which erasing and re-recording are simultaneously performed by a single beam is also possible. In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase.

As a recording layer material used in such a phase change recording method, a chalcogen alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system, Ag-
Attempts have been made to use In—Sb—Te alloy thin films and the like.

[0007]

However, the phase change medium generally has insufficient rewriting characteristics. Particularly, when it is necessary to detect the mark edge, there is a problem that the distribution of the mark length is widened by repeated recording and an error occurs. For example, when the conventional medium is recorded twice as fast as a CD at a speed of 10,000 times, deterioration is severe and many errors occur.

[0008]

The present invention is an optical information recording medium in which at least a phase change recording layer is provided on a substrate, and the recording layer composition is Sb, Te, M (M is Ag, C).
The present invention relates to an optical information recording medium comprising at least one of u and Au) and satisfying the following conditions.

0.7 in (SbxTe1-x) aM1-a
0 <x <0.90, 0 <a <1, and 0 <z <0.33, 0 <b <1 in (MzTe1-z) bSb1-b. (However, it has a phase-change type recording layer on the substrate, and
It has a dielectric layer and the recording layer has a composition represented by the following formula.
However, the activation energy of the recording layer is 3.0 eV or more.
Excludes optical recording media. In the formula _{{(A a B b C c} ) 1-d D d} 1-e M e ( the above formula, A is, Ag and / or Au der
, B is Sb and / or Bi, and C is Te
And / or Se and D is In or In
And Al and / or P, M is Ti, Z
selected from r, Hf, V, Nb, Ta, Mn, W and Mo
At least one element selected. Also, a, b,
c, d and e represent atomic ratios, and 0 <a ≦ 0.20 0.6 ≦ b <10 0 <c <0.40 a + b + c = 1, 0 <d <0.060 0 ≦ e ≦ 0.20 Is))

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The SbTe-based recording layer has become a stable compound with Sb2Te3 and has a sufficiently high crystallization rate, so that it has been attracting attention as a phase change medium from an early stage. However, there are problems that the crystallization rate is not always appropriate, the crystallization temperature is low, and the storage stability is poor.

Therefore, it is common to slow the crystallization rate and obtain an appropriate crystallization temperature by adding an excess of Sb to the mixture of Sb ₂ Te ₃ and GeTe. However, by adding a considerable excess of Sb to Sb ₂ Te ₃ , there is a composition range that can satisfy the characteristics of both the crystallization rate and the crystallization temperature, and it is possible to obtain a disk with excellent repetitive recording characteristics. Can

It is already well known that the crystallization rate becomes slower when Sb is added to Sb ₂ Te ₃ . However, according to the conventional study, Sb ₇₀ Te ₃₀ (at.%)
It was carried out in a composition range with a small amount (Head 1-27733).
8). When the amount of Sb is larger than that of Sb ₇₀ Te ₃₀ , the crystallization rate becomes faster again.

In this composition range, the crystallization rate becomes faster as the amount of Sb increases. When the rotation speed of the disk changes, the appropriate crystallization speed also changes, but by changing the Sb amount, a composition corresponding to the rotation speed of the disk can be obtained. The X-ray analysis shows that the crystal has a strong peak of Sb rather than Sb ₂ Te ₃ , and this point is also fundamentally different from the conventional system.

The reason why the crystallization rate behaves in this way is not always clear, but good characteristics are obtained near the eutectic point of Sb and Sb ₂ Te ₃ or in a composition range in which Sb is more than that. When Sb is crystallized, Sb ₂ T
It is considered that e ₃ controls the ease of incorporation into the crystal site.

Experimentally, as described above, the crystallization becomes faster as the amount of Sb increases in this composition range. However, if the amount of Sb is too large, the storage stability is not good. In the Sb-Te system, the eutectic point of Sb and Sb ₂ Te ₃ was 70 at. % Composition.

Therefore, in SbxTe1-x, 0.7
0 <x <0.90 is good. The addition of additives makes it possible to control the crystallization temperature, the crystallization speed, and the like.
At least one element selected from Ag, Cu, and Au is preferable as an additive element to this system.

Although the optimum Sb amount changes as the amount of the additive increases, it is preferable that the ratio of the Sb amount and the Te amount is not changed or the Sb amount is slightly increased to obtain the same initial characteristics.
However, if the amounts of Ag, Cu, and Au are too large, the repetitive recording characteristics deteriorate. Accordingly, 0.70 <x <0.90 and 0 <a <1 in (SbxTe1-x) aM1-a, and 0 <z <0.3 in (MzTe1-z) bSb1-b.
Excellent characteristics can be obtained in the composition range represented by 3, 0 <b <1.

That is, the composition range is surrounded by the following four compositions A, B, C and D, and does not include the composition on the boundary line. A: Sb _0.7 Te _0.3 , B: Sb _0.9 Te _0.1 , C: Ag
_0.476 Sb _0.367 Te _0.157 , D: Ag _0.233 Sb _0.690 T
e _{0.077 In} addition, 3 at. % Or less may be included.

As a layer structure, a dielectric protective layer is formed on the substrate,
In general, a phase transition type optical recording layer, a dielectric protective layer, and a reflective layer are laminated in this order. It is necessary to select the film thickness of each layer so that the signal strength becomes large. Further, in order to control the ease of recrystallization after melting and the ease of erasing amorphous marks, it is necessary to control the heat conduction by the film thickness of each layer.

For these reasons, the layer structure that gives excellent characteristics is determined. Normally, the phase change optical disk uses the crystalline state as the initial state. It is considered desirable to design the film thickness of each layer such that the reflectance in the crystalline state is larger than the reflectance in the amorphous state so that the reflectance in the unrecorded state, that is, the reflectance in the crystalline state does not become too small.

In this case, the film thickness of each layer that maximizes the reflectance difference between the crystal and the amorphous was calculated. As the complex refractive index of the recording layer, a value measured by an ellipsometer was used. The complex refractive index in the amorphous state at a wavelength of 780 nm was 4.1 to 2.4i, and the crystalline state was 3.2 to 4.4i.

The refractive index of the dielectric protective layer is Ta ₂ O ₅ or (Zn
S) ₈₀ (Si0 _{2) 20} or the like is about 2.1. For the complex refractive index of the reflective layer, the value measured by an ellipsometer is used and is 780
In the case of nm, it was set to 2.1-6.0i. As a result of the calculation, the thickness of the recording layer that maximizes the reflectance difference was around 20 nm, and the thickness of the protective layer between the recording layer and the reflective layer was around 25 nm.

Similarly, 680 nm, 635 nm, 488n
The complex refractive index of each layer was measured even at a laser wavelength of m, and the film thickness showing the maximum reflectance difference at each wavelength was calculated. At 680 nm, the recording layer film thickness was around 20 nm, and between the recording layer and the reflective layer. The protective layer film thickness was around 25 nm. 6
At 35 nm, the thickness of the recording layer is around 20 nm, and the thickness of the protective layer between the recording layer and the reflective layer is around 20 nm.
In m, the thickness of the recording layer was around 18 nm, and the thickness of the protective layer between the recording layer and the reflective layer was around 15 nm.

Therefore, in consideration of shortening the wavelength for high density recording in the future, the recording layer film thickness is 15 to 3
0 nm, the thickness of the protective layer between the recording layer and the reflective layer is 10 to 30
It can be seen that nm is preferable. That is, by selecting these film thicknesses, it is possible to obtain a good reproduction amplitude for a wide range of light source wavelengths with the same layer structure.

If the recording layer or the protective layer between the recording layer and the reflective layer is too thick, the signal amplitude becomes small, and as a result, the jitter also deteriorates. Conversely, even if these film thicknesses are too thin, the same is true. If the thickness of the protective layer is too thin, it is not preferable in that the protective effect is reduced when recording is repeated.

The optically advantageous film thickness thus obtained is such that the thickness of the protective layer between the recording layer and the reflective layer is relatively small,
It has a quenching structure. In the rapid cooling structure, the recrystallized region is usually small and the amorphous mark can be easily written. Furthermore, during erasing (crystallization), the time for which the temperature is kept above the crystallization temperature becomes long, and erasing becomes easy.

The complex refractive indices of the amorphous state and the crystalline state of the recording layer at 680 nm are 3.7-2.
It was 6i and 2.6-4.1i. The complex refractive indexes of the amorphous state and the crystalline state of the recording layer at 635 nm were 3.5-2.7i and 2.3-3.9i, respectively. 48
The complex refractive indices of the amorphous state and the crystalline state of the recording layer at 8 nm are 2.7-2.7i and 1.6-3.2i, respectively.
Met.

The dielectric protective layer material used in the present invention is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion and the like. Generally, Mg, Ca, Sr, Y, La, Ce, Ho, Er, which have high transparency and high melting point,
Yb, Ti, Zr, Hf, V, Nb, Ta, Zn, A
l, Si, Ge, Pb and other oxides, sulfides, nitrides and C
Fluorides such as a, Mg and Li can be used.

These oxides, sulfides, nitrides, and fluorides do not necessarily have to have a stoichiometric composition, and it is also effective to control the composition or mix them for controlling the refractive index and the like. Is. Considering the repetitive recording characteristics, the high refractive index dielectric is preferably a mixture of a plurality of dielectrics based on ZnS.

The reflective layer is preferably a substance having a high reflectance,
Au, Ag, Cu, Al, etc. are used, and Ta, Ti, Cr, Mo, Mg, V, Nb, Zr are used for controlling thermal conductivity.
May be added in small amounts. The substrate of the recording medium in the present invention may be any of glass, plastic, glass on which a photocurable resin is provided, and the like, but a polycarbonate resin is preferable in terms of CD compatibility.

The recording layer, the dielectric layer and the reflective layer are formed by a sputtering method or the like. It is desirable to form a film by an in-line apparatus in which the target for the recording film, the target for the protective film, and if necessary, the target for the reflective layer material are installed in the same vacuum chamber in order to prevent oxidation and contamination between the layers. It is also excellent in terms of productivity.

The recording laser pulse is divided into a plurality of pulses shorter than the recording mark length, and the laser power P3 between the divided recording pulses is smaller than 1/2 of the erasing power.
A laser power (P3) other than zero is recommended. However, since it is necessary to apply focus servo and tracking servo, it is preferable that at least the laser power P3 is larger than the reproduction power (usually 0.3 to 1 mW). Normally, the laser power P3 is set to 0.3 mW or more.

By doing so, recrystallization of the recording mark after melting can be prevented and the recording power margin can be widened. This effect becomes smaller when the laser power between the divided pulses becomes larger than half the erasing power.
For example, when recording a 6T mark of the EFM modulation method, the division method may be divided into 4 to 6 pulses.

Since the temperature of the tip portion of the mark does not easily rise, it may be preferable to make the leading divided pulse 2 to 4 times longer than the other divided pulses. An example of the divided pulse pattern is shown in FIG. When recording the 6T mark of the EFM modulation method, it is preferable that the divided pulse pattern has a waveform as shown in FIG. 1, for example.

In FIG. 1, the pulse length T1 of the divided pulse
The interval T2 between the divided pulses is preferably T1 + T2 = T. Further, when T1 is shorter than T2, recrystallization of the recording mark can be prevented more effectively. That is,
It may be better to set T1 ≦ T2. However, T1 is 0.
It must be greater than 1T. If it is less than 0.1T, the previously recorded amorphous mark cannot be erased.

[0036]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
The layer is 200 nm, the Ag ₆ Sb ₆₇ Te ₂₇ layer is 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk.

After initializing this disc, an EFM random signal was repeatedly recorded at 2.8 m / s using an optical disc evaluation device (laser wavelength 780 nm, NA 0.55) to measure the jitter of the 3T mark. Recording power 12m
The laser pulse waveform shown in FIG. 1 was used with W and erasing power of 6 mW. 3T mark jitter at first recording is 9n
s It was 13 ns after recording was repeated 10,000 times.

Example 2 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
The layer is 200 nm, the Cu ₆ Sb ₆₇ Te ₂₇ layer is 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk.

After initializing this disk, an EFM random signal was repeatedly recorded at 2.8 m / s using an optical disk evaluation device (laser wavelength 780 nm, NA 0.55) to measure the jitter of the 3T mark. Recording power 12m
The laser pulse waveform shown in FIG. 1 was used with W and erasing power of 6 mW. 3T mark jitter at first recording is 9n
s It was 12 ns after recording was repeated 10,000 times.

Example 3 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
Layer is 200 nm, Au ₈ Sb ₆₇ Te ₂₅ layer is 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk.

After this disc was initialized, an optical disc evaluation device (laser wavelength 780 nm, NA 0.55) was used to record a signal of 2.9 Mhz at 5.6 m / s and a duty of 50% with a recording power of 15 mW and an erasing power of 6 mW. When done, the CNR was 53 dB. 2000
After repeated recording 0 times, the CNR was 52 dB, which was not deteriorated.

Example 4 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
The layer is 200 nm, the Ag ₅ Sb ₇₁ Te ₂₄ layer is 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk.

After this disc was initialized, an optical disc evaluation device (laser wavelength 780 nm, NA 0.55) was used to record a signal of 2.9 Mhz at 5.6 m / s and a duty of 50% with a recording power of 15 mW and an erasing power of 6 mW. When done, the CNR was 52 dB. 2000
After repeated recording 0 times, the CNR was 52 dB, which was not deteriorated.

Comparative Example 1 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
200nm layer, Ag _{1 4} Sb ₆₄ Te ₂₂ layer to 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk.

The recording layer was obtained by simultaneously sputtering two targets of AgSbTe ₂ and Sb. After initializing this disc, an optical disc evaluation device (laser wavelength 7
EF at 2.8 m / s using 80 nm, NA 0.55)
The M random signal was repeatedly recorded and the jitter of the 3T mark was measured.

The recording power was 10 mW and the erasing power was 5 mW, and the laser pulse waveform shown in FIG. 1 was used. The 3T mark jitter at the time of the first recording was 9 ns, but after the recording was repeated 5000 times, it was 15 ns.

Comparative Example 2 (ZnS) ₈₀ (SiO ₂ ) ₂₀ on a polycarbonate substrate
The layer is 200 nm, the Ag ₁₁ Sb ₆₉ Te ₂₀ layer is 20 nm,
A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 100 nm were sequentially laminated by a magnetron sputtering method, and further an ultraviolet curable resin was provided to a thickness of 4 μm to prepare a disk. The recording layer was obtained by simultaneously sputtering two targets of AgSbTe ₂ and Sb.

After this disc was initialized, an optical disc evaluation device (laser wavelength 780 nm, NA 0.55) was used to record a signal of 2.9 Mhz at 5.6 m / s and a duty of 50% with a recording power of 15 mW and an erasing power of 6 mW. When done, the CNR was 51 dB. But 2
After the recording was repeated 0000 times, the CNR decreased to 48 dB.

[0049]

By using the optical information recording medium of the present invention, a phase change optical disk having excellent initial signal characteristics and repetitive recording characteristics can be obtained. These characteristics are superior to the conventional ones, and can be practically used as a rewritable optical disk in the future. In particular, it is also useful as a rewritable type optical disc using the CD format and a rewritable type of a digital video disc.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a divided pulse pattern.

[Explanation of symbols]

Pulse length of T1 split pulse Interval between T2 split pulses

Continuation of front page (56) Reference JP-A-2-249686 (JP, A) JP-A-1-100746 (JP, A) JP-A-60-179954 (JP, A) JP-A-8-224961 (JP , A) JP-A-6-12674 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41M 5/26 G11B 7/24 511

Claims (3)

(57) [Claims] 1. An optical information recording medium having at least a phase change recording layer provided on a substrate, wherein the recording layer composition is S.
An optical information recording medium comprising b, Te, and M (M is at least one element of Ag, Cu, and Au) and satisfying the following conditions. (SbxTe1-x) a M1-a 0.70 <x <0.
90, 0 <a <1, and 0 <z <0.33, 0 <b <1 in (MzTe1-z) bSb1-b (however, a phase-change recording layer is provided on the substrate, On the recording layer
It has a dielectric layer and the recording layer has a composition represented by the following formula.
However, the activation energy of the recording layer is 3.0 eV or more.
Excludes optical recording media. In the formula _{{(A a B b C c} ) 1-d D d} 1-e M e ( the above formula, A is, Ag and / or Au der
, B is Sb and / or Bi, and C is Te
And / or Se and D is In or In
And Al and / or P, M is Ti, Z
selected from r, Hf, V, Nb, Ta, Mn, W and Mo
At least one element selected. Also, a, b,
c, d and e represent atomic ratios, and 0 <a ≦ 0.20 0.6 ≦ b <10 0 <c <0.40 a + b + c = 1, 0 <d <0.060 0 ≦ e ≦ 0.20 Is)) 2. The optical information recording medium according to claim 1, wherein at least a dielectric protective layer, a phase change recording layer, a dielectric protective layer, and a reflective layer are laminated in this order on a substrate.
An optical information recording medium, wherein the recording layer has a thickness of 15 to 30 nm, and the dielectric protective layer between the recording layer and the reflective layer has a thickness of 10 to 30 nm. 3. A method of performing one-beam overwrite recording on the optical information recording medium according to claim 2 by using at least the recording laser power P1 and an erasing laser power P2 smaller than P1 and forming a mark. The recording pulse is divided into a plurality of pulses shorter than the mark length, and the laser power of each divided pulse is the recording laser power P1.
And the laser power between the divided pulses is a laser power P3 which is mainly less than 1/2 of the erasing laser power P2 and is not zero.