JP2003257081A - Phase transition optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase transition optical recording medium having a high erasure rate at a high linear speed, high recording sensitivity and high stability of a recording mark. <P>SOLUTION: In the phase transition optical recording medium wherein information is recorded and erased by utilizing reversible phase transition between a crystal phase and an amorphous phase of a recording layer, a protective layer consists of a film which is constituted of (1) any one or more of oxides and (2) any one or more of carbides and wherein each element other than oxygen of the oxides which constitute the protective layer has an XPS peak position (n) of 0.01 to 0.7, if the peak position at the time when the element is the stoichiometric composition of the oxide and the peak position at the time when the element is of a single form are defined as 0 and 1, respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical information recording medium for recording, reproducing and erasing information by a laser beam or the like.

[0002]

2. Description of the Related Art A phase change type optical disk is a kind of rewritable optical recording disk and records information by a reversible phase change (mostly between crystal and amorphous) of a recording layer. Optical modulation overwriting is possible with a single-layer recording film by a single head, and a signal is read by a change in reflectance due to a phase change, so high compatibility with existing optical recording disks such as CD-ROMs is high. Due to such features as described above, research and development have been actively conducted in recent years as a rewritable optical recording disk, and it is applied to a rewritable DVD.

In a phase change optical recording medium such as a phase change type optical recording disk, recording is generally performed by forming a recording mark of an amorphous phase by a laser beam on a crystalline phase (erased state) of a recording layer. A reproduction signal is obtained by detecting the difference in reflectance between the amorphous phase and the amorphous phase. Moreover, by modulating the intensity of the laser beam during signal recording between the intensity of amorphization (peak power) and the intensity of crystallization (bias power) (see FIG. 1), a single beam, a single layer Light modulation overwrite (Direct Overwrite: DO
W) is possible, and a recording disk having a large capacity and a high transfer rate can be obtained.

[0004]

In the phase change optical recording medium, direct overwrite (DOW) is possible as described above, and by using an oxide as a protective layer, the erasing rate characteristic at high linear velocity is improved. . However, when an oxide is used as the protective layer, the recording sensitivity is lowered, and high power is required for signal recording.

The present invention has a good erasing rate at high linear velocity,
It is an object of the present invention to provide a phase change optical recording medium having high sensitivity and good recording mark stability.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies in view of the above-mentioned situation, the present inventors have formed a multilayer film including a protective layer and a recording layer on a substrate, and Utilizing the reversible phase change between crystalline phase and amorphous phase,
In a phase change optical recording medium for recording and erasing information,
It was found that by forming the protective layer from a film made of a specific component, the recording sensitivity is high, and the erasing rate at a high linear velocity is improved. Further, by making the component ratio of the protective layer within a specific range, The inventors have found that the effect is improved, and further found that the stability of the recording mark is improved by controlling the film forming atmosphere, thus completing the present invention.

That is, according to the present invention, a multilayer film including a protective layer and a recording layer is formed on a substrate, and the reversible phase change between the crystalline phase and the amorphous phase of the recording layer is utilized to transfer information. In a phase-change optical recording medium for recording and erasing, the protective layer is composed of at least one substance selected from oxides and at least one substance selected from carbides, and at least one oxide of the oxides. When the element other than oxygen is A, the peak position of the X-ray photoelectron spectroscopy spectrum (XPS) of A of the oxide forming the protective layer is n, and A is the value when A forms the oxide stoichiometrically. When the XPS peak position of is 0 and the single XPS peak position of A is 1,
The present invention relates to a phase change optical recording medium, wherein n is in the range of 0.01 to 0.7 and the protective layer is formed in contact with the recording layer.

The protective layer preferably contains at least one oxide of an element of the following group A.

Group A: Ta, Al, Nb, Si, Ti Further, it is desirable that the above-mentioned protective layer contains at least one kind of carbide of the elements of the following group B.

Group B: Ta, Al, Nb, Si, Ti Further, the content of carbide in the protective layer is 1 to 40 mo.
It is preferably 1%, more preferably 1 to 30 m.
ol%, more preferably 1 to 25 mol%.

Further, it is desirable that the recording layer is made of an alloy of Ge, Sb and Te or a material containing this alloy as a main component.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

FIG. 2 is a partial sectional view showing the structure of an example of the phase change optical recording medium of the present invention. In the phase change optical recording medium of FIG. 2, a first protective layer 22, a recording layer 23, a second protective layer 24, and a reflective layer 25 are laminated on a substrate 21.

The substrate 21 is not particularly limited as long as it is sufficiently transparent in the wavelength range of the laser to be used and satisfies the properties as a medium substrate such as mechanical properties, and glass, polycarbonate, amorphous polyolefin or the like is used. it can.

The first protective layer 22 and the second protective layer 24
Is composed of one or more substances selected from oxides and one or more substances selected from carbides, and when A is an element that is not oxygen in at least one oxide of the oxides, the protective layer is The peak position of the X-ray photoelectron spectroscopy spectrum (XPS) of A of the constituent oxides is n, the peak position of XPS of A when A forms a stoichiometric oxide is 0, and the peak position of XPS of A alone is When the peak position is 1, n
Is a film composed of a substance having a range of 0.01 to 0.7.

For example, in the case of tantalum oxide shown in FIG. 8, T of Ta ₂ O ₅ in which Ta forms a stoichiometric oxide.
When the XPS peak position of a is 0 and the XPS peak position of metal tantalum is 1, the Ta of the oxide forming the protective layer is
The XPS peak position n of is calculated.

As will be described later, the n is 0.0
By using a substance in the range of 1 to 0.7, it is possible to obtain a phase change optical recording medium having an excellent balance between recording sensitivity and erasing rate and good recording mark stability. The more preferable range of n is 0.1 to 0.7, and the more preferable range is 0.2 to 0.6.

The value of n can be controlled by changing the sputtering gas during film formation to an oxidizing atmosphere or a reducing atmosphere.

By adding a carbide to the protective layer, high sensitivity can be obtained without deteriorating the erasing rate characteristic, but it is considered that this is because low thermal conductivity is involved.

XP only when the value of n is 0.7 to 1
A film having an S peak has low light transmittance and is not desirable for use as a protective layer of an optical recording medium.

The protective layer preferably contains at least one oxide of an element of the following group A, and preferably contains at least one carbide of an element of the following group B.

Group A: Ta, Al, Nb, Si, Ti Group B: Ta, Al, Nb, Si, Ti The total content of carbides contained in the protective layer is 1 to 40 mo.
1% is preferable, 1 to 30 mol% is more preferable,
More preferably, it is in the range of 1 to 25 mol%. If the content exceeds 40 mol%, the extinction coefficient (k) of the film may increase, the transparency deteriorates, and it becomes unrealistic as a phase change optical recording medium.

The recording layer 23 includes a GeSbTe-based thin film, I
A film having a reversible phase change such as an nSbTe-based thin film can be used, but it is preferable to use an alloy of Ge, Sb and Te or a material containing this alloy as a main component. The recording layer and at least one protective layer are formed in contact with each other. By forming the recording layer and the protective layer in contact with each other, crystal nucleation is promoted at the contact surface (interface), and crystallization proceeds faster. GeSb as recording layer
A Te-based thin film, an InSbTe-based thin film, or the like can be used. However, since crystallization of the GeSbTe-based thin film is mainly caused by nucleation, it is particularly useful as a recording layer of the phase-change optical recording medium of the present invention having the protective layer. preferable.

The reflective layer 25 is made of a film having a high reflectance in the wavelength range of the laser used, such as an Al alloy or an Ag alloy.

The first protective layer and the second protective layer serve to protect the recording layer as well as enhance the light absorption efficiency to the recording layer,
In addition, since it also has a role of increasing the amount of change in reflected light before and after recording, these thicknesses are designed to be optimum in consideration of the laser wavelength used, the film thickness of the recording layer, and the like.

In addition to the above structure, the phase change optical recording medium of the present invention uses the above protective layer only for the first protective layer or the second protective layer, and the other protective layer is made of another substance. Or a so-called surface reproduction type optical recording medium in which the order of film formation is reversed.

The above first protective layer, second protective layer, recording layer,
The reflective layer can be formed by a vacuum film forming technique such as a DC sputtering method, an RF sputtering method, or a vacuum evaporation method.

Furthermore, after forming these layers, a protective coat layer made of synthetic resin or the like may be formed thereon, if necessary.

[0029]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

(Example 1) As shown below, FIG.
A phase change optical recording medium having a structure as shown in was manufactured. 0.
A first protective layer 32 is formed on a disc-shaped substrate 31 made of polycarbonate in which grooves having a width of 7 μm are formed at a pitch of 1.4 μm.
(Thickness: 100 nm) 3 TaC materials (10 mmφ) and 3 SiC materials (10 mm square) were placed on a Ta ₂ O ₅ target (4 inchφ), and a mixed gas of argon and oxygen was used as a sputtering gas. It was formed by RF sputtering. After this, Ge ₂ Sb ₂ Te
_The recording layer 33 composed of ₅ (film thickness: 20 nm) was formed into Ge ₂ Sb ₂
It was formed by DC sputtering of a Te ₅ alloy target. Further, a second protective layer 34 (film thickness: 20 nm) was formed by RF sputtering under the same conditions as the first protective layer. After that, the reflective layer 35 (film thickness: 100 nm) is set to A
It was formed by DC sputtering a 1-3 wt% Cr target. An ultraviolet curable resin having a thickness of 10 μm was formed thereon as a protective coat layer 36 to complete a phase change optical recording medium.

Phase-change optical recording media having the above structure were prepared by changing the mixing ratio (volume ratio) of the mixed gas atmosphere of argon and oxygen when forming the protective layer (Samples 1 to 7 of Example 1). .

When a sample having the protective layer formed in Example 1 and having a thickness of 0.5 μm formed under the same conditions was measured by XPS, the presence of Ta ₂ O ₅ , TaC and SiO _x was confirmed.

Comparative Example 1 A phase change optical recording medium was prepared in the same manner as in Example 1 except that a mixed gas of argon and oxygen of 65:35 (volume ratio) was used as the sputtering gas.

Comparative Example 2 Example 1 was repeated except that a mixed gas of argon and hydrogen was used as the sputtering gas.
A phase change optical recording medium was prepared in the same manner as in.

(Comparative Example 3) Only a Ta ₂ O ₅ target was used when forming the first protective layer and the second protective layer, and argon: oxygen was 98: 2 (volume ratio) as a sputtering gas.
A phase change optical recording medium was produced in the same manner as in Example 1 except that the mixed gas of No. 1 was used.

Example 2 Instead of the Ta ₂ O ₅ target at the time of forming the first protective layer and the second protective layer, an Al ₂ O ₃ target (Example 2 sample 1) and an Nb ₂ O ₅ target (Example ₂ ) were used. 2 sample 2), SiO ₂ target (Example 2 sample 3), TiO ₂ target (Example 2 sample 4), In ₂ O ₃ target (Example 2 sample 5),
A MgO target (Example 2 sample 6), a ZrO ₂ target (Example 2 sample 7), and a ZnO target (Example 2 sample 8) were used, and the protective layer was used as a sputtering gas with argon and oxygen of 98: 2 (volume). Example 1 except that it was formed using a mixed gas of
A phase change optical recording medium was prepared in the same manner as in.

Example 3 The TaC material at the time of forming the first protective layer and the second protective layer was a SiC material (Example 3 sample 1), an Al ₄ C ₃ material (Example 3 sample 2), and a TiC material ( Sample 3 of Example 3), NbC material (Sample 4 of Example 3), ZrC material (Sample 5 of Example 3), and a mixed gas of 98: 2 (volume ratio) of argon and oxygen as a sputtering gas for the protective layer. A phase change optical recording medium was produced in the same manner as in Example 1 except that the phase change optical recording medium was formed.

(Embodiment 4) The TaC material and the SiC material at the time of forming the first protective layer and the second protective layer are made of only the SiC material, the number of the SiC materials is changed, and the sputtering gas is argon: oxygen: 98: 2. A phase change optical recording medium was prepared in the same manner as in Example 1 except that the mixed gas (volume ratio) was used (Samples 1 to 8 in Example 4).

(Example 5) In the recording layer, Ge ₁ Sb ₂ Te ₄ (Example 5 sample 1), G was used instead of Ge ₂ Sb ₂ Te _5.
e ₁ Sb ₄ Te ₇ (Example 5 sample 2), AgInSb
Te alloy (Ag: 4 atom%, In: 6 atom%,
Sb: 61 atom%, Te: 29 atom%) (Example 5 sample 3), the first protective layer and the second protective layer were used as sputtering gas, and argon and oxygen were 98: 2.
A phase change optical recording medium was produced in the same manner as in Example 1 except that the mixed gas (volume ratio) was used.

(Example 6) Second protective layer 34 (film thickness: 20)
The nm) using a ZnS-20mol% SiO ₂ target was formed only by RF sputtering using Ar as a sputtering gas, a first protective layer 32 (film thickness: 100
nm) on a Ta ₂ O ₅ target (4 inch φ) with TaC
3 materials (10mmφ) and SiC material (10mm
3 corners), 98: 2 argon to oxygen (volume ratio)
A phase change optical recording medium was produced in the same manner as in Example 1 except that RF sputtering was performed using the mixed gas of.

(Example 7) First protective layer 32 (film thickness: 10)
(0 nm) using a ZnS-20 mol% SiO ₂ target and using only Ar as a sputtering gas.
The second protective layer 34 (film thickness: 20 is formed by sputtering.
nm) on a Ta ₂ O ₅ target (4 inch φ) with TaC
3 materials (10mmφ) and SiC material (10mm
3 corners), 98: 2 argon to oxygen (volume ratio)
A phase change optical recording medium was produced in the same manner as in Example 1 except that RF sputtering was performed using the mixed gas of.

(Embodiment 8) The order of film formation on the substrate is as follows: reflective layer (film thickness: 100 nm), first protective layer (film thickness: 20 n).
m), recording layer (film thickness: 20 nm), second protective layer (film thickness:
100 nm), and a surface reproduction type phase change optical recording medium having a reverse structure was prepared in the same manner as in Example 1 except that a protective coating layer having a thickness of 0.1 mm was formed thereon.

(Comparative Example 4) First protective layer 32 (film thickness: 10)
0 nm) and the second protective layer 34 (film thickness: 20 nm) with Z
A phase change optical recording medium was produced in the same manner as in Example 1 except that the nS-20 mol% SiO ₂ target was used and only argon was used as the sputtering gas to form the film by RF sputtering.

The phase change optical recording media of Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to initial crystallization of the recording layer using an initialization device.

Next, an amorphous mark having a length of 0.6 μm was recorded at a linear velocity of 6 m / s on the track in the crystallized region of the recording layer (recording pitch: 1.2 μm, laser wavelength: 680 nm, NA: 0.55). At the time of this recording, a laser modulation pattern to which an off pulse is added as shown in FIG. 4 is used, the off pulse power (Poff) and the reproduction power (Pr) are 1 mW, the peak power width is 50 ns, and the off pulse width is 33 ns. Bias power (Pb) is 5mW and peak power (Pb)
p) was changed to record an amorphous mark, and Pp that maximizes the CNR was set as the optimum Pp (Pp ₀ ). Then P
Amorphous marks were recorded with b = 5 mW and Pp = Pp ₀ , and the amorphous marks were erased by irradiating laser beams of various powers. At this time, the difference between the carrier levels before and after erasing was measured as the erasing rate, and the laser power that maximizes the erasing rate was defined as the optimum Pb (Pb ₀ ). Next, Pp is (Pp ₀ -1) mW and Pb is (Pb ₀ -1) m
Amorphous mark as W (mark length: 0.6 μm)
Is recorded and erased with a (Pb ₀ -1) mW laser.
This recording / erasing was performed 20 times per track (hereinafter, this step is referred to as initialization processing).

For the initialized track, Pb =
As Pb ₀ mW, an amorphous mark (mark length: 0.6 μm) was recorded at a linear velocity of 6 m / s. In addition, 0.6μ at a linear velocity of 6m / s for the initialized track.
Amorphous mark of m length is Pr = 1mW, Pof
Recording was performed with a laser power of f = 1 mW, Pp = Pp ₀ , and Pb = Pb ₀ (recording pitch: 1.2 μm), this recording mark was erased with the erasing power, and the difference in carrier level before and after erasing was taken as the erasing rate It was measured.

Argon of sputtering gas: 9 oxygen
CNR of sample 5: 5 (Sample 4 of Example 1)
FIG. 5 shows the recording power (Pp) dependency (hereinafter referred to as a power curve) of the above. The intersection point where the power curve intersects CNR = 30 dB was defined as the recording sensitivity (Pth) of each sample.

In Example 1, the XPS peak positions (n) and recording sensitivities (Pth) of Ta and Si when the ratio of sputtering gas argon to oxygen was changed from 100: 0 to 65:35, and the linear velocity was 12 m. Table 1 shows the erasing rate at / s
Shown in. If the erasing rate is 25 dB or more, there is no problem in practical use, and 28 dB or more is more preferable.

[0049]

[Table 1] From Table 1, the protective layer of the present invention has favorable characteristics in terms of the balance between recording sensitivity and erasing rate as compared with the comparative example.
Even better characteristics are obtained when the XPS peak position of Si is in the range of 0.2 to 0.6. Further, as shown in Comparative Example 1, those having a peak position of XPS exceeding 0.7 have low recording sensitivity and small erasing rate.

The samples of Examples 1-7 were placed in a constant temperature bath maintained at a temperature of 80 ° C., and the time (T _{−2 dB} ) in which the CNR decreased by 2 dB from the initial value before the addition was measured. The same measurement was performed at 90 ° C and 70 ° C, with the horizontal axis representing temperature and the vertical axis representing T.
Fig. 6 shows the one created using the logarithmic value of _{-2 dB} . Figure 6
In, the T _{−2 dB} at room temperature (25 ° C.) was obtained by extrapolation. The same measurement was performed on the other samples of Example 1, the samples of Comparative Example 1 and the sample of Comparative Example 2, and the horizontal axis indicates S.
The value of n obtained by the XPS measurement of i, T on the vertical axis at 25 ° C.
Figure 7 shows the one created using the logarithmic value of _{-2 dB} .

From FIG. 7, from the viewpoint of recording mark stability,
It can be seen that when n is 0.01 or more, T _{−2 dB} has a value that _poses no practical problem. Further, even if it is 0.7 or more, T _{-2 dB} shows a good value, but as shown in Table 1, since it is inferior in terms of recording sensitivity and erasing rate, the value range of n is 0.0.
It can be seen that 1 to 0.7 is effective.

Also, for Examples 2 and 3, Pth and erase ratio and XPS measurement of Si were performed. The results are shown in Tables 2 and 3, respectively. In addition, the measurement results of the samples of Example 1, Sample 3, Comparative Example 3, and Comparative Example 4 are also shown for comparison.

[0053]

[Table 2]

[Table 3] It can be seen from Tables 2 and 3 that the protective layer of the present invention has a higher erasing rate than the comparative example. In addition, Ta, Al, Nb, Si or Ti
Containing any of the oxides of Ta, Al, N
It can be seen that the inclusion of carbides of b, Si, or Ti improves the balance between the erasing rate characteristics and the recording sensitivity, and is particularly good.

For Example 4 and Comparative Example 3, P
Th and erasure rate were measured. The results are shown in Table 4.
For comparison, the measurement results of the sample of Comparative Example 3 are also shown.

[0055]

[Table 4] The composition of SiC was determined by EPMA or fluorescent X-ray analysis of the protective layer formed under the same conditions. Further, when the XPS measurement of Si was performed on the sample of Example 4, the value of n was in the range of 0.4 to 0.6. From Table 4, it can be seen that when the amount of SiC is in the range of 1 to 40 mol%, the erasing property and the recording sensitivity are in good balance, and 1 to 25 mol
It is particularly good in the range of%.

Table 5 shows the results of measuring the erasing rate for Example 5. Table 5 also shows the measurement results of the sample of Example 1 and the sample of Comparative Example 4 for comparison.

[0057]

[Table 5] From this result, GeS is better than that of AgInSbTe system recording layer.
It can be seen that the bTe recording layer has a higher erasing rate.

Table 6 shows the results of measuring the erasing rate for Examples 6 and 7. Table 6 also shows the measurement results of the sample of Comparative Example 4 for comparison.

[0059]

[Table 6] From these results, it can be seen that if either the first protective layer or the second protective layer has the protective layer defined in the present invention, good erasing rate characteristics can be obtained.

A recording / reproducing test was conducted on the sample of Example 8, and it was confirmed that a good CNR and an erasing rate were obtained, and that the sample could be used as a surface reproducing optical recording medium.

[0061]

According to the present invention, high recording sensitivity and
There is little unerased residue at high linear speeds, and good erasure rate characteristics,
A phase change optical recording medium having excellent recording mark stability can be obtained, and a phase change type optical disk having a high transfer rate and good recording mark stability can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship of laser power of a recording / reproducing apparatus.

FIG. 2 is a partial cross-sectional view showing the structure of an example of the phase change optical recording medium of the present invention.

FIG. 3 is a partial cross-sectional view showing a structure of a phase change optical recording medium of Examples and Comparative Examples of the present invention.

FIG. 4 is a diagram showing a relationship between laser powers used for recording marks of 0.6 μm.

5 is a graph showing the CNR peak power dependence of the sample of Example 1. FIG.

FIG. 6 is a diagram showing the temperature dependence of the time for which the CNR of the sample of Example 1 decreases by 2 dB.

FIG. 7: 25 ° C. of each sample of Example 1 and Comparative Examples 1 and 2
It is the figure which plotted the time when CNR in FIG.

FIG. 8 is a Ta oxide, Ta ₂ O ₅ and T constituting a protective layer.
It is a figure which shows the relationship of the XPS peak position of a metal.

[Explanation of symbols]

21, 31: substrate 22, 32: First protective layer 23, 33: recording layer 24, 34: Second protective layer 25, 35: reflective layer 36: Protective coat layer

Claims (5)

[Claims] 1. A phase change optical recording medium in which a multilayer film including a protective layer and a recording layer is formed on a substrate to optically record, erase, and reproduce information, and the protective layer is selected from oxides. An oxide that forms a protective layer, which is composed of a film composed of one or more kinds of substances and one or more kinds of substances selected from carbides, where A is an element other than oxygen in at least one of the oxides. The peak position of the X-ray photoelectron spectroscopy (XPS) of the product A is n, the peak position of XPS of A when A forms a stoichiometric oxide is 0, and the peak of XPS of A alone When the position is 1, n
Is in the range of 0.01 to 0.7, and the protective layer is formed in contact with the recording layer. 2. The phase change optical recording medium according to claim 1, wherein the protective layer contains at least one oxide of an element of group A below. Group A: Ta, Al, Nb, Si, Ti 3. The protective layer contains at least one or more carbides of the following Group B elements.
The phase change optical recording medium according to item 1. Group B: Ta, Al, Nb, Si, Ti 4. The total content of carbides in the protective layer is from 1 to 40.
It is mol%, The phase change optical recording medium of any one of Claims 1-3. 5. The phase change according to claim 1, wherein the recording layer is made of an alloy of Ge, Sb and Te, or a material containing the alloy as a main component. Optical recording medium.