JP2553736B2 - Optical recording medium and method of manufacturing optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium capable of recording / reproducing and erasing information with high density and large capacity by using a laser beam or the like.

2. Description of the Related Art Optical recording media have attracted attention as large-capacity and high-density memories, and currently, a rewritable type capable of erasing and re-recording information is under development. As one of the rewritable optical recording media, a Te-Ge-Sb alloy thin film is used as a recording layer, and the recording layer is heated by laser irradiation, melted, and rapidly cooled to record information by amorphizing. In some cases, information is erased by crystallization by heating and gradually cooling this. FIG. 3 is a sectional view showing a conventional rewritable optical recording medium. In FIG. 3, a first protective layer 12 made of a dielectric material, a recording layer 13, a second protective layer 14 made of a dielectric material, and a metal thin film are provided on a substrate 11 made of a transparent resin material on a disk having a central hole. Forming the reflective layer 15,
A protective plate 17 is provided on top of this with an adhesive 16. Here, if a Te—Ge—Sb alloy thin film is used for the recording layer 13, this crystallization speed is high, so that it is possible to amorphize and crystallize only by modulating and irradiating the intensity of a single laser.
Therefore, this rewritable optical recording medium is capable of rewriting information by a single laser beam generally called overwrite.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In an optical recording medium capable of recording and erasing information by using means for heating and heating a recording thin film to melt and amorphize it, and to heat and anneal slowly cooling and crystallization, many recording and erasing operations are performed. The signal quality may fluctuate corresponding to the repetition of times. Possible causes of this change are thermal damage to the recording layer itself and thermal damage to the disk substrate or protective layer due to rapid heating and cooling at 400 ° C. or higher due to laser light. Further, in the recording layer, a so-called segregation, which is a local change in the composition and components in the layer, may occur depending on the constituent composition. When the above changes occur, deterioration such as increase in noise occurs during repeated recording / reproduction / erasing. As a measure against these, for example, if a mixture of GeTe, Sb ₂ Te ₃ , and Sb is used as the material of the recording layer,
By adjusting the amount of Sb appropriately, fluctuations in signal quality due to a large number of recording / erasing repetitions were prevented. This is due to the fact that Sb becomes
This is because it has a blocking effect on the phase separation of Sb ₂ Te ₃ minutes. With this concept, a stable signal was obtained even when recording / erasing was repeated 10 ⁵ times or more. However, when the order of 10 ⁶ times is repeated, the recording layer material sandwiched between the protective layers pulsates in response to thermal expansion / contraction of the protective layer due to repeated heating / cooling associated with repeated recording / erasing, and It may move along the guide groove in the rotational direction. When such a phenomenon occurs, there is a problem in that the recording layer is uneven in thickness and the signal quality is deteriorated.

Regarding the erasing characteristics, the amorphous film containing Te has a typical melting point in a wide temperature range of 400 to 900 ° C. By irradiating these recording thin films with laser light and gradually increasing the temperature by cooling. Can be crystallized. This temperature is generally in the crystallization temperature range below the melting point. When the crystallized film is irradiated with laser light of a high power level and heated to a temperature higher than its melting point, that part is melted and rapidly cooled, and then amorphized again to form marks. When amorphization is selected as the recording mark, this mark is formed by melting and rapidly cooling the recording thin film, so the faster the cooling rate, the more uniform the amorphous state is obtained and the signal amplitude is improved. To do. When the cooling rate is slow, a difference occurs in the degree of amorphization between the center and the periphery of the mark. Next, at the time of crystallization erasing, the amorphous mark portion which has already been recorded by the irradiation of laser light is heated to a crystallization temperature or higher and gradually cooled to be crystallized to erase the mark.
At this time, when the marks are crystallized uniformly, the erasing property is improved. However, if the recording marks are not uniform,
The reflectance and absorptance of the recording marks are likely to be uneven,
When erasing, there was a problem that the crystallization state became non-uniform, unerased recording marks occurred, and the erasing characteristics deteriorate. An object of the present invention is to provide an optical disc having stable cycle characteristics and good recording / erasing characteristics.

Means for Solving the Problems The present invention is one in which a state is changed by irradiation with laser light or the like, and a recording layer made of a material containing nitrogen in a mixture of GeTe, Sb2Te3, and Sb is formed on a substrate. Is.

Function The present invention has the above-described structure, that is, by forming a material containing nitrogen in a mixture of GeTe-Sb2Te3-Sb on a substrate, recording by repeating heating / cooling accompanying repeated recording / reproduction / erasing. The phenomenon in which the layer material pulsates and moves along the guide groove can be suppressed, and thereby the repetitive recording / erasing characteristics can be improved.

A first protective layer, a recording layer made of a material containing nitrogen in a mixture of GaTe, Sb ₂ Te _3, and Sb, a second dielectric layer, and a reflective layer are provided on the substrate. Since the second dielectric layer is thinner than the first protective layer and has a thickness of 30 nm or less, the reflective layer made of metal and the recording layer are brought close to each other, the recording layer is rapidly cooled, and the recording mark is in an amorphous state. Becomes as a result,
Recording / erasing is improved.

Example An optical recording medium according to an example of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention. In FIG. 1, a first protective layer 2 made of ZnS—SiO _{2 having} excellent heat resistance is previously formed on a transparent substrate 1 on a disk having a central hole. The composition ratio is about SiO ₂ content
20 mol% and the film thickness is about 150 nm. 3 is a recording layer G
eTe, Sb ₂ Te ₃ , Sb is a thin film mixed with nitrogen, and the film thickness is about 2
It is 0 nm. The second protective layer 4 is made of the same material as the first protective layer 2 and has a film thickness of about 20 nm. Reference numeral 5 is a reflective layer made of an Al alloy and has a film thickness of about 100 nm. A protective plate 6 is attached to the substrate 1 with an adhesive 7. Recording layer 3
As the composition of GeTe, Sb2Te3, Sb among the materials constituting the above, the inside of both lines of b = Sb / Sb2Te3 = 0 and b = 1.0 is selected in the triangular diagram of GeTe, Sb2Te3, Sb in FIG. . In the composition region in which b was less than 0, that is, in the composition region containing excess Te, the effect of preventing local segregation was lower than that of the composition containing excess Sb, which is the composition of this example. Further, in the composition region exceeding b = 1.0, amorphization deterioration is likely to occur during repeated recording / erasing. Therefore, the composition region of 0 ≦ b ≦ 1.0 is preferable because of good repeatability.

For g = GeTe / Sb ₂ Te ₃ , when g is 0.5 or less,
The crystallization transition temperature decreases, and the heat resistance stability decreases. g
In the composition region exceeding 2.3, the thermal stability is good but the sensitivity decreases. Therefore, 0.5 ≦ g ≦ 2.3 is good and preferable.

As a method of forming the first and second protective layers, the recording layer and the reflective layer, generally, vacuum deposition or sputtering can be used. In this embodiment, the sputtering method using a mixed gas of argon and nitrogen is used as the method of forming the recording layer. At this time, the partial pressure of nitrogen is important for determining the characteristics or film quality, but the partial pressure of nitrogen during sputtering of the recording thin film is 10 ^-5 to 1.
A range of 0 × 10 ^-4 Torr is suitable. The reason for this is that when the nitrogen partial pressure is smaller than 10 ^-5 Torr, the amount of nitrogen contained in GeTe, Sb2Te3, Sb decreases, and the material of the memory layer 3 pulsates and prevents the phenomenon of moving along the guide groove. The effect becomes smaller. On the other hand, if the nitrogen partial pressure is higher than 10 ^-4 Torr, changes in optical characteristics such as the refractive index of the recording layer, or crystallization speed, amorphization speed, and other basic characteristics related to recording / erasing Will change. Therefore, the nitrogen partial pressure is 10 ^{-5 to} 1.0 × 1
A suitable range is 0 ^-4 Torr.

In the ZnS—SiO ₂ mixed film of the first and second protective layers 2 and 4, the SiO ₂ ratio is set to 20 mol%, but the present invention is not limited to this. However, if the ratio of SiO ₂ is 5 mol% or less,
Effect obtained when a mixture of SiO ₂ to ZnS, ie the effect of reducing the crystal grain size becomes small, and when it exceeds 40 mol%, since those properties of the SiO ₂ film is increased, the SiO ₂ ratio Is appropriately in the range of 5 to 40 mol%.

Further, the film thickness of the second protective layer 4 is made as thin as about 30 nm. By this, the reflective layer 5 and the recording layer 3 to be the heat diffusion layer are formed.
And the heat of the recording layer 3 at the time of recording / erasing is rapidly transferred to the reflective layer 5, so that the recording layer 3 is rapidly cooled and the recording mark becomes a uniform amorphous state. As a result,
Erasure is improved.

With the disk configuration of this embodiment, an outer diameter of 130 mm, a rotation of 1800 rpm, a linear velocity of 8 m / sec, a signal of f1 = 3.43 MHz, and an overwrite characteristic of f2 = 1.25 MHz were measured. As a result, the recording signal
The C / N ratio was 55 dB or higher, and the overwrite erase rate was 30 dB or higher. Regarding the overwrite cycle characteristics, the bit error rate characteristics were measured, and as a result, no deterioration was found for 10 ⁶ cycles or more.

As described above, according to the present invention, recording is performed by forming a recording layer in which GeTe, Sb2Te3, and Sb are mixed with nitrogen on the substrate.
It is possible to suppress the phenomenon that the recording layer material moves along the guide groove with the repetition of erasing, thereby improving the repetitive characteristics of recording and erasing. Also, by using a quenching structure in which the protective layer between the recording layer and the reflective layer is thin,
It is possible to provide an optical recording medium in which uniform amorphization is possible, recording / erasing characteristics are good, and rewriting is possible 10 ⁶ or more times.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical recording medium according to an embodiment of the present invention,
FIG. 2 is a triangular diagram showing the composition of GeTe, Sb2Te3, Sb in the recording layer of the optical recording medium in the example of the present invention,
FIG. 3 is a sectional view of a conventional optical recording medium. 1 ... Substrate, 2 ... First protective layer, 3 ... Recording layer, 4 ...
… Second protective layer, 5 …… Reflective layer, 6 …… Protective plate, 7 ……
adhesive.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Yoshi ▼ Kazumi Oka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-63-228433 (JP, A) JP JP-A-1-290135 (JP, A) JP-A-1-302549 (JP, A) JP-A-61-44693 (JP, A) JP-A-2-56746 (JP, A) JP-A-1-116937 (JP , A)

Claims (9)

(57) [Claims] 1. An optical recording medium in which a state is changed by irradiation with laser light or the like, and a recording layer made of a material containing nitrogen in a mixture of GeTe, Sb ₂ Te ₃ and Sb is formed on a substrate. 2. An optical recording medium, characterized in that a recording layer made of a mixture of GeTe, Sb ₂ Te ₃ and Sb containing nitrogen is formed by a sputtering method using a mixed gas of argon and nitrogen. Manufacturing method. 3. The nitrogen partial pressure when forming the recording layer is 10 ^-5 to 10
3. The method for manufacturing an optical recording medium according to claim 2, wherein the range is ⁻⁴ Torr. 4. The composition of the recording layer has a GeTe / Sb ₂ Te ₃ molar ratio of g.
The optical recording medium according to claim 1, wherein 0.5 ≦ g ≦ 2.3. 5. The optical recording medium according to claim 1, wherein the composition of the recording layer is 0 ≦ b ≦ 1.0, where the molar ratio of Sb / Sb ₂ Te ₃ is b. 6. The composition of the recording layer has a molar ratio of GeTe / Sb ₂ Te ₃ of g.
_2. The optical recording medium according to claim 1, wherein the range is 0.5 ≦ g ≦ 2.3, and 0.1 ≦ b ≦ 1.0, where b is the molar ratio of Sb / Sb ₂ Te ₃ . 7. A first protective layer, GeTe and Sb ₂ Te ₃ on the substrate.
An optical recording medium in which a recording layer made of a material containing nitrogen in a mixture of Sb, a second protective layer, and a reflective layer are sequentially formed. 8. A first dielectric layer, GeTe and Sb ₂ Te ₃ on a substrate.
A recording layer made of a material containing nitrogen in a mixture of Sb and Sb,
A second protective layer and a reflective layer are provided, and the second protective layer is the first
The optical recording medium according to claim 7, wherein the second protective layer has a thickness of 30 nm or less. 9. The optical recording medium according to claim 7, wherein the first and second protective layers are a mixture of ZnS and SiO ₂ , and the SiO ₂ ratio is 5 to 40 mol%.