JPH0920072A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the rewriting characteristics of a phase change recording medium by incorporating a precipitation phase made of matrix of Ge and Te elements and specific compound crystal in a recording layer. SOLUTION: The optical recording medium has a recording layer for recording, erasing or reproducing information by varying optical properties by emitting laser onto a board. The recording layer contains a parent phase made of Ge, Sb or Te element, and a precipitation phase represented by a symbol A, and the composition is represented by a formula (GeTe)1- x-(Sb2 Te3 )x }1-y-z Sby A2 (where A is a compound crystal made of Al element and at least element of Sb or Te, x, y, z are the numbers of ranges indicated by 0.3<=x<=0.7, 0<=y<=0.1, 0.01<=z<=0.3). The A is, for example, the compound crystal of AlSb, Al2 Te3 , thereby improving rewriting characteristics, and reducing the initializing times by laser emitting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording, reproducing and erasing information by using laser light.

[0002]

2. Description of the Related Art In recent years, rewritable optical discs for recording, reproducing and erasing information by irradiating laser light have been attracting attention as the amount of information has increased. Rewritable optical discs include a magneto-optical recording method that utilizes the magneto-optical effect and a phase-change recording method that utilizes a phase transition between amorphous and crystalline materials. This phase-change method requires an external magnetic field. Instead, it has the advantage that overwriting can be performed only with the laser intensity.

Chalcogenides have been mainly studied as a phase change recording material. For example, materials described in US Pat. No. 3,217,591 of 1966 and Japanese Patent Laid-Open No. 61-137784 are used. There is. Among them, Ge-Sb
-Te ternary material has already been industrialized because it can be crystallized at high speed and its rewriting property is superior to other materials.
In this ternary system, there exist ternary compound phases such as GeTe and Sb ₂ Te ₃ and ternary compound phases such as Ge ₂ Sb ₂ Te ₅ , GeSb ₂ Te ₄ and GeSb ₄ Te ₇ on the line connecting the _two. But especially Ge ₂ Sb ₂ Te ₅ and GeSb
It is said that the composition containing 3 to 5% of Sb in ₂ Te ₄ is suitable for the recording / erasing characteristics.

[0004]

However, on the other hand, on the other hand,
In a phase change recording medium, the so-called number of times of rewriting, in which recording / erasing is repeated many times, is poor. Therefore, in order to improve this, a medium structure was devised in which the recording layer and the dielectric layer between the recording layer and the heat sink layer were thinned (T.Ohta et al., Proc. SPIE, 10
78, 27 (1989)). Although the rewriting characteristics have been improved considerably by this, the mark edge recording method for forming a long bit is not sufficient yet.

As one of the main causes of the deterioration of the rewriting characteristics, it is considered that the film thickness changes due to the flow of the recording film. This occurs because stress is generated when the recording film is made amorphous, and the melted recording film is pushed out. Various attempts have been made to prevent this phenomenon. For example, formation of a nitride (Japanese Patent Laid-Open No. 04-10979) and a high melting point compound Cr ₂ T
The addition of e ₃ (Proceedings of the 6th Phase Change Recording Workshop Symposium, (1994) 87) can be mentioned. However, although it was confirmed that the number of rewrites was improved by adding Cr ₂ Te ₃ , in this case, the initial process of pre-irradiating light with high power 3000 times is required. It is considered that this is because Cr has a high melting point and Cr ₂ Te ₃ crystals are hard to precipitate in the film.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an optical recording medium which solves the above-mentioned problems, which is Ge-Sb.
It is characterized in that compound crystals such as AlSb and Al ₂ Te ₃ are finely precipitated in the Te-based recording layer. That is, the present inventor has variously studied the rewriting characteristics of a phase change recording medium using a conventional Ge-Sb-Te-based material, the recording of information by changing the optical characteristics on the substrate at least by laser light irradiation, Has a recording layer for erasing and reproducing,
The recording layer contains a matrix phase composed of Ge, Sb, and Te elements and a precipitation phase represented by the symbol A, and the composition is represented by the formula {(GeTe)
_{1-x (Sb 2 Te 3} ) x} 1-yz Sb y A z ( However, A is a more becomes crystalline compound with any of the elements of at least Sb and Te as Al element, x, y, z are respectively 0.3 ≤x≤0.7, 0≤y
The outline is an optical recording medium represented by ≤ 0.1, 0.01 ≤ z ≤ 0.3), and the mark edge recording method is adopted by using A as a compound crystal such as AlSb or Al ₂ Te _3. The present invention has been completed by discovering that the rewriting characteristics in 1) are significantly improved as compared with the conventional Ge-Sb-Te recording layer, and the number of initializations by laser light irradiation can be significantly reduced.

This will be described in more detail below. The present invention relates to an optical recording medium, which has a recording layer thin film for recording, erasing and reproducing information by changing the optical characteristics on at least a laser beam on a substrate as described above. The layer contains a matrix phase composed of Ge, Sb, and Te elements and a precipitation phase represented by the symbol A, and its composition is represented by the formula {(G
_{eTe) 1-x (Sb 2} Te 3) X} 1-yz Sb y A z (A, x, y,
In the optical recording medium represented by z above, z is A
Is a compound crystal consisting of an Al element and at least one element selected from Sb and Te, and A is, for example, a binary compound crystal such as AlSb or Al ₂ Te ₃ or a compound phase thereof. And AlSb formed on the line connecting Sb ₂ Te ₃
It is characterized by being a ternary compound crystal such as Te ₃ .

The structure of the optical recording medium of the present invention is, as shown in FIG. 1, a structure in which a first dielectric layer, a recording layer, a second dielectric layer and a reflective layer are sequentially formed on a substrate. It consists of The substrate, the dielectric layer, and the reflective layer constituting this optical recording medium may be the same as known ones, and therefore, the substrate is made of glass or a transparent resin such as polycarbonate, polyolefin, or polymethylmethacrylate. The dielectric layer should be ZnS, SiO ₂ , Al ₂ O ₃ , SiN, A in consideration of the durability and enhancement effect of the recording layer.
AlN, Cu, Au, Ag, Pt or alloys containing these may be used because ceramics such as lN and SiC, or a mixture thereof, may be used, and the reflective layer has high reflectance and thermal conductivity. These layers may be formed by a sputtering method, a vacuum evaporation method, or the like. Furthermore, an organic protective layer made of an ultraviolet curable resin or the like may be formed thereon.

For the parent phase forming the recording layer of the present invention, a Ge-Sb-Te ternary alloy conventionally used as a phase change material is used. This material is excellent in high-speed crystallization and stability in the amorphous region, which are necessary conditions for overwriting. However, in order to obtain more optimal properties, its composition should be expressed by the formula {(GeTe) _{1 -x (Sb 2 Te 3) X} } 1-y Sb y in x, y, respectively 0.3 ≦ x ≦ 0.7, it is necessary to limit the range of 0 ≦ y ≦ 0.1.

In the present invention, as the precipitation phase A in this recording layer
The compound phase such as AlSb and Al ₂ Te ₃ is finely dispersed and precipitated, but even when the mother phase undergoes a crystalline-amorphous phase change, this precipitated phase A does not melt or transform. , It is necessary to be retained as a solid phase. Ratio z of this precipitation phase A
Is less than 0.01, there is no effect, and the larger the value is, the more the flow of the recording layer at the time of melting can be prevented, but if it exceeds 0.3, the reproduction signal amplitude decreases and good characteristics cannot be obtained. The ratio z needs to be 0.01 ≦ z ≦ 0.3, and preferably 0.05 ≦ z ≦ 0.2.

The recording layer is formed by a thin film forming method such as a sputtering method or a vapor deposition method. In the case of the sputtering method, the target is Ge-Sb-with the same ratio as the above film composition.
A Te-Al alloy may be used, or a composite target in which a compound chip such as AlSb or Al ₂ Te ₃ is placed on a Ge-Sb-Te alloy target may be used. Alternatively, Al, Sb, or Te chips can be used. The film immediately after film formation was in a uniform amorphous state, and compound A was not precipitated in the film.However, by performing an initial melting process by laser light irradiation as an initial step, compound A was formed as a crystalline phase. Relatively quickly Ge
-Sb-Te disperse and precipitate in the matrix to form precipitate phase A. The condition of the initial process is that the disk is rotated at v = 6m / s and the wavelength is
Laser light with DC power of 10 mW or more at 780 nm, NA 0.5 several times
The compound phase may be precipitated by irradiating several tens of times.

There are two points of the present invention, and the first point is
Al element has almost no solid solubility in Sb and Te, which are the elements that make up the matrix, and the maximum solubility in Ge is 1.5.
It is about at.%. For this reason, Al acts in the direction of forming a precipitated phase by combining with Sb and Te rather than forming a solid solution in the parent phase.

The second point is that the melting points of the Al, Sb and Te elements forming the precipitated phase are not too high as compared with the melting point of the parent phase. Ge
As shown in Fig. 2, the -Sb-Te matrix has a melting point of around 600 ° C. On the other hand, the melting points of the elements such as Al, Sb, and Te that form the precipitation phase are 660, 630, and 450 ° C, respectively, and even the highest Al element is only 30 ° C higher than the melting point of 630 ° C of Ge ₂ Sb ₂ Te _5. . Therefore, when the recording layer is melted, these elements form a compound and are precipitated in the mother phase to form a precipitated phase.

The precipitation phase thus formed has a relatively high melting point. For example, the melting points of AlSb and Al ₂ Te ₃ are 10
50 and 895 ° C, which is higher than the melting point of the Ge-Sb-Te matrix by 200 ° C or more. Therefore, even when the mother phase undergoes a phase change between the crystal and the amorphous due to the laser light irradiation, these precipitated phases are not melted and are retained as a solid phase. Since this precipitation phase is uniformly dispersed in the film, it serves to prevent the melted mother phase from flowing.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to Examples and Comparative Examples. Example 1 Using a sputtering apparatus, a first dielectric layer made of a mixture of ZnS and SiO ₂ , a recording layer obtained by adding AlSb to a Ge—Sb—Te alloy, and a first dielectric on a polycarbonate disk substrate on which a group was formed. A second dielectric layer made of the same material as the layer,
The Al reflective layer was sequentially formed. The atmosphere was Ar 5 × 10 ⁻³ Torr, all targets were 4 inches φ, and the film was formed while rotating the substrate. The recording layer was on a Ge ₂ Sb ₂ Te ₅ composition target.
A composite target in which an Al chip and an Sb chip were placed at an atomic ratio of 1: 1 was used, and the AlSb amount in the precipitation phase of the recording layer was adjusted by changing the chip amount. The input power is RF 100 W,
The film was formed so that the film thickness would be 300 Å. As a result of ICP analysis, the composition of the mother phase of the recording layer was x = 0.33, and the value of y varied with the amount of chips, but was within 0.1 in all cases.

The disk is rotated at v = 6 m / s and the wavelength is 780 n.
An initial step of precipitating a compound phase was performed by irradiating a laser beam with a DC power of 10 mW or more at m 2, NA 0.5 several times to several tens of times. Next, after crystallizing the entire recording layer with a laser beam of DC power 6 mW, recording power 10 mW, erase power 5 mW, frequency 1 MHz,
50% Duty and 2.7MHz frequency, Duty
The signal was repeatedly recorded at 50%, and the carrier value (C) and the erasing rate were measured. FIG. 3 shows the carrier value according to the AlSb composition ratio z normalized by the carrier value at z = 0.
The carrier decline rate at z = 0.3 is about 10%,
Above that, it drops sharply. From this, the ratio of AlSb is 0.
It can be seen that 01 ≦ z ≦ 0.3 is good. Also, 6 in FIG. 4 shows AlSb.
The change in the erasure rate when the signal is repeatedly recorded with the composition ratio z = 0.2 is normalized by the first erasure rate.

Example 2 Instead of Al and Sb chips, Al and Te chips were used in an atomic ratio of 2: 3.
Was carried out in the same manner as in Example 1 except that the proportion of
A film containing Al ₂ Te ₃ as a precipitation phase was obtained. The measurement result of the erasing rate of this film formation is shown in 7 of FIG.

Example 3 The same procedure as in Example 1 was carried out except that Al, Sb, and Te chips were placed at an atomic ratio of 1: 1: 1 instead of Al and Sb chips. A film containing a compound of Sb and Te was obtained. The measurement result of the erasing rate of this film formation is shown in 8 of FIG.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that Al and Sb chips were not placed. The measurement result of the erasing rate of this film formation is shown in 9 of FIG.

Comparative Example 2 A film was formed under the same conditions as in Example 1. However, when the initial step of precipitating the compound phase immediately after the film formation was not carried out and the AlSb phase was not sufficiently precipitated, the erasing rate of this film formation was found to be comparative example 1.
The same result was shown.

From the results shown in FIG. 4, it can be seen that in Examples 1 to 3, the erasing rate was less likely to decrease than in Comparative Example 1 and the rewriting characteristics were improved.

[0022]

According to the present invention, the rewriting characteristics of the phase change recording medium are remarkably improved by finely precipitating compound crystals such as AlSb and Al ₂ Te _{3 in} the Ge-Sb-Te recording layer. The effect has improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a layer structure of an optical recording medium according to the present invention.

FIG. 2 is a pseudo binary system equilibrium diagram of GeTe—Sb ₂ Te ₃ .

FIG. 3 is a diagram showing a change in carrier value according to the ratio of AlSb in a recording film.

FIG. 4 is a diagram showing a change in erasing rate with the number of recording / erasing repetitions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st dielectric material layer 3 ... Recording layer 4 ... 2nd dielectric material layer 5 ... Reflective layer 6 ... Example 1 7 ... Example 2 8 ... Example 3 9 ... Comparative example 1

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Tawara 3-2-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Shin-Etsu Chemical Co., Ltd. Corporate Research Center

Claims (3)

[Claims] 1. A substrate has a recording layer for recording, erasing, and reproducing information at least by changing optical characteristics by laser light irradiation, and the recording layer has a mother phase composed of Ge, Sb, and Te elements. and a precipitation phase represented by the symbol a, and its composition formula _{{(GeTe) 1-x (} Sb 2 Te 3) x} 1-yz Sb y a z ( However, a is at least Sb and Al element A compound crystal composed of one of Te and x, y, and z are 0.3 ≦ x, respectively.
≤0.7, 0≤y≤0.1, 0.01≤z≤0.3). 2. The melting point of the precipitation phase A is 200 ° C. higher than the melting point of the mother phase.
The optical recording medium according to claim 1, which is higher than the above. 3. The precipitation phase A is not accompanied by melting and transformation between crystalline and amorphous during recording, erasing and reproduction of information by laser light irradiation, and only the parent phase is transformation between crystalline and amorphous. The optical recording medium according to claim 1, which comprises: