JPH11250498A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent changes in the compsn. of a phase transition material in a recording film as much as possible by forming a metal film comprising a material containing elements selected from a phase transition material on the surface of a recording film facing to a substrate or on the surface opposite to this surface. SOLUTION: A first dielectric film 3, a recording film 4, a metal film 5, a second dielectric film 6, a light reflecting film 7 and a protective film 8 are formed in this order on a substrate 2. The metal film 5 consists of a metal material containing elements selected from structural elements of the phase transition material which forms the recording film 4, and elements having tendency to segregate and decrease in the phase transition material which constitutes the recording film 4 when recording is repeated. When the phase transition material in the recording film 4 is Ag-In-Sb-Te, metal film 5 is preferably made of Sb. Even when segregation is produced in the phase transition material due to the inhomogeneous temp. distribution in the recording film 4 to render the compsn. distribution inhomogeneous, the metal element in the fused metal film 5 compensates the loss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording film made of a phase-change material in which a phase change between a crystalline state and an amorphous state is caused by irradiation of a light beam, formed on a substrate. The present invention relates to an optical recording medium that optically records and erases information signals by causing a phase change by irradiation. In particular, the present invention relates to a recording film containing Ag as a phase change material, and relates to an optical recording medium having improved durability.

[0002]

2. Description of the Related Art As an optical recording medium, for example, a phase change type optical recording medium comprising a recording film made of a phase change material which undergoes a phase change between a crystalline state and an amorphous state upon irradiation with a light beam is formed on a substrate. There is a recording medium. This phase change type optical recording medium is
A phase change occurs in the recording film due to the irradiation of the light beam, and an information signal is recorded on the recording film.

More specifically, this phase-change optical recording medium 50
Is, as shown in FIG. 6, a first dielectric film 5 on a substrate 51.
2, recording film 53, second dielectric film 54, light reflecting film 55,
The protection film 56 is formed sequentially.

The main components of the phase change material constituting the recording film 53 of such a phase change type optical recording medium 50 are, for example, Ge-Te, Ge-Te-Sb, In-Sb-T
So-called chalcogen-based alloy materials such as e, Ge-Sn-Te, Ag-In-Sb-Te are known. In particular, JP-A-62-53886 and JP-A-63-225934.
No. JP-A-3-80635 and JP-B-8-32482.
In the gazette of Japanese Patent Application Laid-open No.
A material in which the composition ratio of b-Te is specified is disclosed. Also, JP-A-4-232779 and JP-A-6-1662.
No. 68 discloses an Ag-I for improving durability.
A material having a specified composition ratio of n-Sb-Te is disclosed.

Further, Japanese Patent Laid-Open No. 5-140883 reports that an oxide film is provided between the recording film 53 and the dielectric film 54 for the purpose of improving durability. Japanese Patent Application Laid-Open No. Hei 6-36352 is directed to an optical recording medium using a chalcogen compound containing Ge as a material of the recording film 53, and a heat diffusion layer between the recording film 53 and the dielectric film 54. It has been reported that durability is improved by providing a metal film having a film thickness of 1 to 5 nm containing Si or Ge or both elements.

[0006]

The above-mentioned A
A phase-change optical recording medium using a chalcogen material containing Ag (hereinafter, referred to as an Ag-based chalcogen compound) such as g-In-Sb-Te as a phase-change material is Ge-Te.
And the like, the recording / reproducing linear velocity is lower than that of a phase change type optical recording medium using a chalcogen material containing Ge (hereinafter, referred to as a Ge-based chalcogen compound) as a phase change material. There is an advantage that erasing can be performed efficiently, the erasing rate is higher, and the signal amplitude can be larger.

However, the phase change type optical recording medium using the Ag-based chalcogen compound cannot obtain signal characteristics sufficiently corresponding to high linear velocity and high density, and has poor recording durability. It is insufficient, and sufficient improvement has not been achieved by the methods disclosed in the related art. In particular, in a phase-change optical recording medium using this Ag-based chalcogen compound, when recording and erasing are repeated, the recording film is broken from the end of the area where a series of signals have been written, or the initial characteristics of the recording film cannot be maintained. However, there is a major drawback in that an error occurs or a reproduction signal faithful to a recording signal cannot be obtained, that is, a so-called repetitive deterioration phenomenon is very likely to occur.

This repeated deterioration phenomenon occurs for the following reason.

In a phase-change optical recording medium, the recording film is heated by laser light irradiation, and recording is performed through a molten state. At this time, in the recording film, a region irradiated with the laser beam changes from a crystalline state to an amorphous state, and an information signal is recorded.

When such recording is repeated, the temperature distribution of the recording film due to the laser irradiation becomes non-uniform, and due to the non-uniform temperature distribution, the constituent elements of the recording film diffuse and move in the direction of the recording track, and A phenomenon in which the constituent elements are locally concentrated and increased or diluted and decreased, so-called segregation occurs.

[0011] The segregation of the constituent materials of the recording film changes the phase change conditions in the crystalline state and the non-crystalline state. As a result, it is difficult to perform recording and reproduction under the recording conditions suitable for the initial composition of the recording film. , Causing repeated deterioration.

Particularly, in a phase change type optical recording medium in which the phase change material of the recording film is an Ag-based chalcogen compound, since the repetitive deterioration phenomenon is very likely to occur, improvement of the repetitive recording durability is strongly demanded.

In view of the above, the present invention has been proposed in view of the conventional situation, and uses a chalcogen compound containing Ag as a phase change material of a recording film, and achieves an improvement in repeated recording durability. It is another object of the present invention to provide an optical recording medium having excellent recording and reproducing characteristics.

[0014]

SUMMARY OF THE INVENTION An optical recording medium according to the present invention, which has been completed to achieve the above-mentioned object, comprises a phase-change material which undergoes a phase change between a crystalline state and an amorphous state upon irradiation with a light beam. A recording film made of is formed on a substrate, and a light beam is applied to the recording film to cause a phase change to record an information signal on the recording film.

In particular, in the optical recording medium according to the present invention, the recording film is made of a phase change material containing at least Ag,
A metal film made of a material containing an element selected from the phase change material is formed on at least one of the surface of the recording film facing the substrate or the surface opposite to the surface. It is characterized by the following.

Thus, the optical recording medium according to the present invention is
Even if the phase change material of the recording film diffuses and moves due to non-uniform temperature distribution in the recording film during repeated recording, segregation occurs in this phase change material. The metal element in the film compensates. as a result,
The optical recording medium to which the present invention is applied is controlled so that the composition of the phase change material of the recording film does not change as much as possible even if recording is repeatedly performed, so that recording and erasing can be repeated in a good state.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. Hereinafter, a phase change optical disk will be described as an optical recording medium to which the present invention is applied. FIG. 1 shows a phase change optical disk 1 to which the present invention is applied.
FIG. 2 is an enlarged cross-sectional view showing a main part of FIG.

The phase-change optical disk 1 to which the present invention is applied
As shown in FIG. 1, a first dielectric film 3, a recording film 4, a metal film 5, a second dielectric film 6, a light reflecting film 7, and a protective film 8 are formed on a disk-shaped substrate 2 in this order. It is formed by lamination.

In particular, the magnetic recording medium 1 to which the present invention is applied
Has a metal film 5 made of a material containing an element selected from the constituent elements of the recording film 4 on the recording film 4.

The substrate 2 has a groove 2b formed along one recording surface on one main surface 2a. The thickness of the substrate 2 is, for example, 0.6 mm. Examples of the substrate 2 include a plastic substrate made of a synthetic resin such as polycarbonate (PC) and polymethyl methacrylate (PMMA), and a glass substrate. Substrate 2
Is formed by, for example, injection molding or a photopolymer method (2P method).

The first dielectric film 3 is formed on the substrate 2. As a material of the first dielectric film 3, for example, Z
_{nS, SiO X, Al 2 O} 3, ZrO 3, Ta 2 O 5, Si 3
N ₄ , SiN _x , AlN _x , MoO ₃ , WO ₃ , ZrO ₂ , B
N, TiN, ZrN, PbF ₂ , MgF _{2 and the} like.
These materials are used alone or as a mixture. Among them, preferred as the material of the first dielectric film 3 is a material containing at least ZnS, and more preferably, a ZnS-SiO _2.

The thickness of the first dielectric film 3 is 80 n
It is preferably from m to 140 nm. As a method for forming the first dielectric film 3, for example, a conventionally known method such as a vapor deposition method or a sputtering method such as ion beam sputtering, DC sputtering, or RF sputtering can be used.

The recording film 4 is an optical recording layer formed on the first dielectric film 3 and capable of writing and erasing information signals by irradiation with a light beam such as a laser beam. More specifically, the recording film 4 is made of a phase change material that reversibly changes phase between a crystalline state and an amorphous state by irradiation with a light beam, and the phase change material is irradiated with a light beam to cause a phase change. Thus, recording and erasing of the information signal are performed.

In particular, the phase change material used for the recording film 4 of the present invention is an Ag-based chalcogen compound, for example, Ag-In-Sb-Te, Ag-In-Se-Te.
And the like. in this way,
The phase-change optical disc 1 to which the present invention is applied uses an Ag-based chalcogen compound as the material of the recording film 4, so that the erasing rate is good and the signal amplitude can be made large.

The recording film 4 has a thickness of 18 nm to 30 nm.
It is preferably nm. As a method for forming the recording film 4, for example, a vapor deposition method, ion beam sputtering, DC
A conventionally known method such as a sputtering method such as sputtering or RF sputtering can be used.

In the phase change optical disk 1 to which the present invention is applied, a metal film 5 is formed on one main surface 4a of the recording film 4.
In particular, the metal film 5 is formed of a metal material containing an element selected from constituent elements of the phase change material forming the recording film 4. Here, as the material of the metal film 5, an element which tends to segregate and decrease among the phase change materials constituting the recording film 4 during repeated recording may be used.

Specifically, the phase change material of the recording film 4 is Ag
In the case of -In-Sb-Te, the metal film 5 is preferably formed from Sb.

As described above, the phase-change optical disc 1 to which the present invention is applied has the metal film 5 containing the element selected from the constituent elements of the phase-change material forming the recording film 4 on the recording film 4.
Are formed. Therefore, in the phase change optical disk 1 to which the present invention is applied, when recording is repeatedly performed on the recording film 4, segregation occurs in the phase change material due to the non-uniform temperature distribution in the recording film 4, and this phase change occurs. Even if the composition distribution of the material becomes non-uniform, the metal element in the metal film 5 melted by repeated recording will supplement the element reduced by segregation. As a result, the phase-change optical disc 1 to which the present invention is applied can be controlled so that the composition of the phase-change material of the recording film 4 does not change as much as possible even when recording is repeatedly performed. It is possible to repeat the recording, and the recording durability can be improved.

In particular, the phase change material of the recording film 4 is Ag-In
In the phase-change optical disk 1 made of -Sb-Te, Sb segregates due to repetitive recording, and Sb partially segregates, so that the metal film 5 made of Sb is formed on the recording film 4 so as to be melted by repetitive recording. Sb in the metal film 5 can compensate for the Sb segregated and reduced in the recording film 4 and, as a result, the repetitive recording durability is significantly improved.

The thickness of the metal film 5 is 1.5 nm.
Or less, more preferably 0.5 nm
１．０1.0 nm. If the thickness of the metal film 5 is too large, the jitter value of the reproduced signal after the first recording becomes large, and good recording / reproducing characteristics cannot be obtained after repeated recording. Further, if the thickness of the metal film 5 is too small, the effect of minimizing segregation of the phase change material due to repetitive recording does not appear.

The metal film is not limited to being formed on the main surface 4a of the recording film 4 as shown in FIG. 1, but is formed on the main surface 4b of the recording film 4 on the side facing the substrate 2. Alternatively, it may be formed on both main surfaces 4a and 4b of the recording film 4. However, in order to obtain sufficient recording characteristics, especially the initial recording characteristics, the metal film 5 is formed on the main surface 4a of the recording film 4 opposite to the side facing the substrate 2; More preferably, it is sandwiched between the recording film 4 and the second dielectric film 6.

The second dielectric film 6 formed on such a metal film 5 is formed by the same method using the same material as the first dielectric film 3 described above. The thickness of the second dielectric film 6 is preferably 5 nm to 35 nm.

Then, a light reflecting film 7 is formed on the second dielectric film 6. The light reflection film 7 functions as a reflection layer that reflects light incident from the substrate 2 and also functions as a heat sink layer that prevents excessive accumulation of heat in the recording film 4.

As a material of the light reflecting film 7, it is desirable to use a metal element, a metalloid element, a semiconductor element and a compound thereof alone or in combination.
Metal elements such as 1, Au, Ni, Fe, and Cr, and alloys thereof.

The light reflection film 7 has a thickness of 50 n
It is preferably from m to 200 nm. This light reflection film 7
As a method for forming a film, a conventionally known method such as a vapor deposition method or a sputtering method such as ion beam sputtering, DC sputtering, or RF sputtering can be used.

The protective film 8 is formed on the light reflecting film 7. The protective film 8 is formed, for example, by applying a resin such as an ultraviolet curable resin by spin coating, or by bonding a resin plate, a glass plate, a metal plate, or the like to the light reflection film 7 via an adhesive.

The phase change optical disk to which the present invention is applied is not limited to the one that can record, reproduce, and erase from one side as shown in FIG. By pasting them so as to face each other, a structure capable of recording, erasing, and reproducing from both sides may be adopted.

The phase change optical disk 1 configured as described above undergoes an initialization process described below to record information signals,
Erasure and reproduction are performed as follows.

First, on the phase-change optical disk 1, the first dielectric film 3, the recording film 4, the metal film 5, the second
After the dielectric film 6, the light reflecting film 7, and the protective film 8 are formed, an initialization process for initializing the recording film 4 is performed.

This initialization process is to make the recording film 4 a uniform crystalline state before the information signal is recorded on the recording film 4.

More specifically, a predetermined laser beam is uniformly applied to the entire phase change optical disc 1. At this time,
The recording film 4 is heated to a temperature lower than the melting point of the constituent phase change material and higher than the crystallization temperature. After that, the recording film 4 of the phase change optical disk 1 is cooled to be brought into a uniform crystalline state and initialized.

Next, the phase-change optical disk 1 thus initialized is mounted on a recording / reproducing apparatus, and is recorded, erased and reproduced while being rotated at a predetermined linear velocity.

Specifically, when recording an information signal on the phase-change optical disc 1, the recording film 4 is irradiated with a laser beam having a strong power. As a result, the area of the recording film 4 irradiated with the laser beam is rapidly heated to a temperature equal to or higher than the melting point, and then rapidly cooled to an amorphous state, which is an amorphous state. As described above, in the phase-change optical disc 1, the region irradiated with the laser light in the crystalline recording film 4 is in an amorphous state, and an information signal is recorded on the recording film 4 as a recording mark in the amorphous state.

When erasing the information signal recorded on the phase change optical disc 1, at least a recording mark is irradiated with a laser beam weaker than the laser beam irradiated at the time of recording. As a result, the region of the recording film 4 irradiated with the laser beam is heated to a temperature higher than the crystallization temperature and lower than the melting point, and then gradually cooled to a crystalline state regardless of the previous state. As described above, in the recording film 4, an information signal is erased by converting a recording mark in an amorphous state into a crystalline state.

When reproducing the written information signal on the phase-change optical disc 1 on which the information signal is recorded as described above, no phase change of the recording film 4 occurs with respect to the recording film 4. A light beam having a small power is irradiated, and return light of the light beam is received. More specifically, in the phase change optical disk 1, the reflectance when the recording film 4 is in a crystalline state is higher than the reflectance when the recording film 4 is in an amorphous state. Therefore, the recording / reproducing apparatus reproduces the information signal by receiving the return light from the recording film 4 and detecting the difference in the reflectance between the crystalline state and the amorphous state of the recording film 4. Further, the phase change optical disk 1 configured as described above is manufactured, for example, as follows.

First, a substrate 2 on which a predetermined pre-groove is formed by injection molding is manufactured, and then a first dielectric film 3 is formed on the substrate 2 by RF sputtering. Then, a recording film 4 is formed on the first dielectric film 3 by a DC sputtering method.

Next, a metal film 5 is formed on the recording film 4 by a DC sputtering method using a target composed of the constituent elements of the recording film 4.

Next, a second dielectric film 6 is formed on the metal film 5.
Is formed by an RF sputtering method, and then a light reflection film 7 is formed on the second dielectric film 6 by a DC sputtering method. Then, an ultraviolet curable resin is applied and formed on the light reflecting film 7 by a spin coating method, and finally, the phase change optical disc 1 to which the present invention is applied is manufactured.

[0049]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results.

To evaluate the repetitive recording durability of the phase change optical disk to which the present invention was applied, the following phase change optical disk was manufactured.

Example 1 First, a transparent disk-shaped substrate made of a polycarbonate resin having a thickness of 0.6 mm was prepared, and ZnS-2 was placed on the substrate.
A 100 nm-thick first dielectric film was formed by RF sputtering using 0 mol% SiO ₂ .

Next, Ag ₉ I was formed on the first dielectric film.
Using a target made of n ₁₁ Sb ₅₀ Te ₃₀ , Ar gas was flowed into a vacuum apparatus at 70 sccm, the total gas pressure was 4 mTorr, and the film thickness was 26.
A 5 nm recording film was formed.

Next, on this recording film, using a target made of Sb, only Ar gas was flowed into a 70 sccm vacuum apparatus, the total gas pressure was set to 4 mTorr, and
A metal film having a thickness of 0.5 nm was formed by sputtering.

Next, while holding the substrate on which the first dielectric film, the recording film and the metal film are formed in a vacuum, Zn
A 23 nm-thick second dielectric film was formed by RF sputtering using S-20 mol% SiO ₂ .

Next, an Al-Ti film is formed on the second dielectric film.
A light-reflecting film having a thickness of 160 nm was formed by DC sputtering using an alloy, and a phase-change optical disk was manufactured.

Example 2 The thickness of the recording film was 26 nm, and the thickness of the metal film was 1.0 n.
A phase-change optical disc was manufactured in the same manner as in Example 1 except that m was used.

COMPARATIVE EXAMPLE 1 The thickness of the recording film was set to 27 nm. Thereafter, the metal film was not formed on the recording film, and the thickness of the second dielectric film was set to 23 nm.
A phase change optical disk was manufactured in the same manner as in Example 1 except that the above conditions were satisfied.

<Evaluation of Durability of Repeated Recording> The phase change optical disk manufactured as described above was evaluated for the durability of repeated recording as described below.

For each of the phase-change optical disks manufactured in Example 1, Example 2 and Comparative Example 1, first, the linear velocity was measured using a recording / reproducing apparatus having a laser wavelength of 680 nm and an objective lens with a numerical aperture of NA 0.6. Is set to 4.8 m / sec, and the random EFM signal is output once at a predetermined recording power for two times.
Recording and reproduction were repeated 10 times and 100 times.

Next, for each of the phase-change optical disks of Example 1, Example 2, and Comparative Example 1, the recording power was changed and the other conditions were the same, and the random EFM signal was transmitted once,
Recording and reproduction were repeated 10 times and 100 times.

Then, the jitter value of the reproduced signal after repeatedly recording and reproducing each time was measured. Hereinafter, the results of Example 1 are shown in FIG. 2, the results of Example 2 are shown in FIG. 3, and the results of Comparative Example 1 are shown in FIG.

Here, the jitter value is a value obtained by standardizing the standard deviation of each mark edge with respect to the clock by the window width. If this jitter value is about 12.5% or less, the error is considered correctable. Therefore, in the following, this jitter value of 12.5% is used as an evaluation criterion for the media characteristics.

From the results shown in FIG. 4, Comparative Example 1 in which the metal film is not formed on the recording film shows a low jitter value over a wide range of recording power at the time of repeated recording up to ten times. However, in Comparative Example 1, when the recording was repeated 100 times, the jitter value at the lower recording power was significantly increased, and the recording power was 12.5% or less, which is the standard value for the media characteristics. Can be said to be very narrow, and the recording power margin is small.

On the other hand, from the results of FIG. 2 and FIG. 3, the first and second embodiments in which the metal film made of the element selected from the phase change material is formed on the recording film are once and twice. Although the jitter value increases as the recording is repeated, even when recording is repeated 100 times, compared with the comparative example shown in FIG.
11. The jitter value is 12.
5% or less, which means that the recording power margin is large.

From the above results, by forming a metal film made of an element selected from the phase change material of the recording film on the recording film, the repetitive recording durability is improved and the recording power margin is widened. It has been found.

Next, in order to evaluate the relationship between the thickness of the metal film and the jitter value, the following phase change optical disk was manufactured.

Example 3 A phase change optical disk was manufactured in the same manner as in Example 1 except that a recording film having a thickness of 25.5 nm was formed, and a metal film having a thickness of 1.5 nm was formed on the recording film. .

Example 4 A phase change optical disk was manufactured in the same manner as in Example 1 except that a recording film having a thickness of 25.0 nm was formed and a metal film having a thickness of 2.0 nm was formed on the recording film. .

<Evaluation of Relationship between Metal Film and Repeated Recording Durability>
The relationship between the thickness of the metal film and the jitter value was evaluated as described below.

For each of the phase-change optical disks manufactured in Examples 1 to 4 and Comparative Example 1, first, the linear velocity was measured by using a recording / reproducing apparatus having a laser wavelength of 680 nm and an objective lens having a numerical aperture NA of 0.6. Was set to 4.8 m / sec, the recording power was varied, a random EFM signal was recorded and reproduced once at each recording power, and the value with the smallest jitter value at this time was defined as the first bottom jitter value of each phase change optical disc. FIG. 5 shows the initial bottom jitter value of each phase change optical disc.

From the results shown in FIG. 5, the thickness of the metal film is 1.5 n
It was found that when it was larger than m, the initial bottom jitter value was significantly increased. Therefore, when the thickness of the metal film is 1.5
A phase change optical disk having a diameter larger than nm can be said to have a poor repetitive recording durability because the jitter value easily exceeds 12.5% for 100 or more repeated recordings.

From the above results, it was found that in the phase change optical disk to which the present invention was applied, it is preferable that the thickness of the metal film be 1.5 nm or less.

[0073]

As described above in detail, according to the optical information recording medium of the present invention, the recording film is made of a phase change material containing at least Ag, and the surface of the recording film on the side facing the substrate. Alternatively, a metal film made of a material containing an element selected from the phase change material is formed on at least one of the surfaces opposite to the surface.

As a result, the optical information recording medium according to the present invention can reduce the elements which are locally diluted and reduced by segregation even if segregation occurs in the phase change material of the recording film when repeated recording is performed. The metal element in the film compensates.

As a result, in the optical information recording medium to which the present invention is applied, even if the recording is repeatedly performed, the composition change of the phase change material of the recording film can be suppressed as much as possible. Thus, the recording durability is improved, and the recording / reproducing characteristics are high and high reliability is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical information recording medium to which the present invention is applied.

FIG. 2 is a diagram showing experimental results of Example 1.

FIG. 3 is a diagram showing experimental results of Example 2.

FIG. 4 is a view showing experimental results of Comparative Example 1.

FIG. 5 is a diagram illustrating a relationship between a thickness of a metal film and an initial bottom jitter value.

FIG. 6 is a sectional view showing an example of a conventional optical information recording medium.

[Explanation of symbols]

Reference Signs List 1 optical information recording medium, 2 substrate, 3 first dielectric film, 4 recording film, 5 metal film, 6 second dielectric film, 7 light reflection film, 8 protective film

Claims (4)

[Claims] An information signal is recorded by irradiating a light beam to cause a phase change in said recording film, comprising a recording film made of a phase change material in which a phase change between a crystalline state and an amorphous state occurs. In the optical recording medium, the recording film is made of a phase change material containing at least Ag, and a metal made of a material containing an element selected from the elements constituting the phase change material is provided adjacent to the recording film. An optical recording medium having a film formed thereon. 2. The optical recording medium according to claim 1, wherein said phase change material contains Sb, and said metal film is formed of at least Sb. 3. The optical recording medium according to claim 1, wherein said metal film has a thickness of 1.5 nm or less. 4. The substrate according to claim 1, wherein a first dielectric film, said recording film, said metal film, a second dielectric film, and a light reflecting film are sequentially formed on a substrate. Optical recording medium.