JP3010513B2 - Optical recording medium and manufacturing method thereof - Google Patents

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 with a high density and a large capacity by using a laser beam or the like and a method of manufacturing the same.

[0002]

2. Description of the Related Art An optical recording medium has attracted attention as a large-capacity, high-density memory. At present, a rewritable type capable of erasing and re-recording information is being developed. As one of the rewritable optical recording media, Te-G
Using an e-Sb alloy thin film as the recording layer, the recording layer is heated by laser light irradiation, melted, rapidly cooled to become amorphous, and the information is recorded. And erases information. FIG. 2 is a sectional view showing a conventional rewritable optical recording medium. In FIG. 2, a first protective layer 2 made of a dielectric material, a recording layer 3, a second protective layer 4 made of a dielectric material, and a reflection made of a metal thin film are formed on a substrate 1 made of a transparent resin material on a disk having a center hole. In this embodiment, a layer 5 is formed, and a protective plate 7 is provided on the layer 5 with an adhesive 6 interposed therebetween. Here, when a Te—Ge—Sb alloy thin film is used for the recording layer 3, since the crystallization speed is high, 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 with a single laser beam generally called overwrite.

[0003]

However, in an optical recording medium in which information can be stored and erased by heating and raising the temperature of the recording thin film and using means for melting and quenching amorphization and heating and crystallization. -The signal quality may fluctuate in response to a large number of erasures. The cause of this variation is that the laser is repeatedly heated and cooled rapidly at 400 ° C. or higher, causing thermal strain between the second protective layer and the reflective layer, that is, stress due to a difference in linear expansion coefficient due to rapid heating and cooling. And peeling occurs at the interface between the second protective layer 4 and the reflective layer 5. Therefore, the heat of the repetitive laser light accompanied by recording and erasing is trapped in the second protective layer and is destroyed by thermal damage. Also, by peeling off the second protective layer and the reflective layer,
Since the heat for erasing the recording becomes difficult to escape, the recording medium cannot be recorded because it is gradually cooled. When such a change occurs, there is a problem that deterioration such as an increase in noise occurs when recording, reproduction, and erasure are repeated. For erasing characteristics, Te
The amorphous film containing is typically 400 ° C. to 9 ° C.
It has a wide temperature range of 00 ° C. Crystallization can be performed by irradiating these recording thin films with a laser beam and heating and gradually cooling them.
This temperature is generally a crystallization temperature region lower than the melting point. When a laser beam having a high power level is applied to the crystallized film and heated to a temperature higher than its melting point, the portion is melted, rapidly cooled, and then becomes amorphous again to form a mark. If the recording mark is selected to be amorphous, this mark is formed by melting and quenching the recording thin film, so the faster the cooling rate, the more uniform the amorphous state is obtained and the signal amplitude is improved. I do. If the cooling rate is low, 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 laser light irradiation is heated to a temperature higher than the crystallization temperature to be crystallized, and this mark is erased. At this time, when the mark is uniformly crystallized, the erasing characteristics are improved. However, when the state of the recording mark is non-uniform, the reflectivity and the absorptance of the recording mark part tend to be uneven, and when erasing, the crystallization state becomes non-uniform, and the recording mark remains unerased. In addition, there is a problem that the erasing characteristics are deteriorated. The present invention solves the above-mentioned conventional problems, and has stable cycle characteristics.
It is an object of the present invention to provide an optical recording medium having good recording / erasing characteristics.

[0004]

According to the present invention, in order to achieve the above object, a first protective layer is provided on one surface of a transparent substrate,
Irradiation of laser light, etc., absorbs the energy, raises the temperature, melts, rapidly cools, and becomes amorphous. The amorphous state is crystallized by raising the temperature above the crystallization temperature and gradually cooling. sequentially form a recording layer properties, and a second protective layer, and a reflective layer
A formation information rewritable optical recording medium, the oxide of the reflective layer material said second protective layer, or consist of nitrides, oxides towards the reflective layer side from the boundary between the recording layer, Alternatively, the second protective layer and the reflective layer are integrated by providing a composition gradient from a nitride composition to a metal composition. Further, in the present invention, the thickness of the second protective layer is smaller than that of the first protective layer, and the thickness of the oxide or nitride having a stoichiometric composition is 20 nm or more and 30 nm or less. I do. Or the present invention is characterized in that a first protective layer composed of oxide or nitride of the reflective layer. Further, according to the present invention, after forming the second protective layer by a sputtering method using a mixed gas of argon and oxygen or argon and nitrogen, forming a composition gradient by controlling the amount of oxygen or nitrogen gas, It is characterized in that a reflective layer is formed.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention configured as described above, i.e., oxides of reflecting calendar the second protective layer, or composed of nitrides, the interface between the recording layer oxide of a stoichiometric composition, or a nitride, wherein
A composition gradient is provided so as to become a metal composition from the boundary of the recording layer toward the reflective layer side, and the second protective layer and the reflective layer are integrated to form a heating / reproducing system which repeats recording / reproducing / erasing.
The repetition of cooling can prevent the second protective layer and the reflective layer from peeling off, thereby improving the recording / erasing repetition characteristics. In addition, since the thickness of the second protective layer is made thinner than the first protective layer to be 20 nm or more and 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 reduced. It becomes a uniform amorphous state. As a result, the recording / erasing characteristics are improved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical recording medium according to an embodiment of the present invention will be described below with reference to the drawings. Note that the same components as those in the related art have the same reference numerals. FIG. 1 is a sectional view showing an embodiment of the present invention, in which Al (aluminum) is used as a reflection layer.
In FIG. 1, Al ₂ O _3, which is an oxide of Al having excellent heat resistance, is previously placed on a transparent substrate 1 on a disk having a center hole.
The first protective layer 2 made of is formed. The thickness is about 150 nm. Reference numeral 3 denotes a recording layer, and the recording layer 3 is made of Te, Ge, Sb.
Alloys in which the material, for example, GeTe, a Sb ₂ Te ₃
It is a thin film having a thickness of about 20 nm. Reference numeral 4 denotes a second protective layer, which is made of the same material as the first protective layer 2 and has a stoichiometric composition of Al ₂ O ₃ from the interface with the recording layer 3, and goes to the reflective layer side. , A composition gradient is provided so that the metal composition is obtained. When the film thickness of the second protective layer 4 is smaller than 20 nm, the mechanical strength is weakened, the film is destroyed by overwriting of recording and erasing, and the overwriting characteristics are deteriorated. Further, the escape of heat to the reflective layer 5 increases, and the recording sensitivity decreases. On the other hand, when the thickness is larger than 30 nm, the heat of the recording layer 3 hardly escapes and a uniform amorphous mark is hardly formed. Therefore, the thickness of the second protective layer 4 is 20
It is good to set it in the range of nm or more and 30 nm or less. This metal composition, that is, the film thickness of the Al reflecting layer is about 100 nm. Reference numeral 7 denotes a protective plate which is bonded to the substrate 1 with an adhesive 6. Here, the case where the same material is used for the first and second protective layers has been described. However, the present invention is not limited thereto. For example, the first protective layer may be an oxide and the second protective layer may be a nitride. Well, and vice versa. As a method for forming the first and second protective layers, the recording layer, and the reflective layer, generally, vacuum evaporation or sputtering can be used. In this embodiment, as a method for forming the first and second protective layers, a sputtering method using a mixed gas of argon and oxygen is used. Here, when a nitride is used for the protective layer, a mixed gas of argon and nitrogen may be used. The second protective layer 4 and the reflective layer 5 are formed by first performing reactive sputtering with a mixed gas of Ar and oxygen using an Al target to form a layer 4 of Al ₂ O _{3 having} a predetermined thickness, and then forming an oxygen gas. Is formed so that the composition gradient layer 4a of Al ₂ O _X becomes the reflective layer 5 of Al. This Al
Are the reflection layers 5. As described above, the composition of the second protective layer 4 is made to have a composition gradient from the oxide composition to the metal composition from the recording layer 3 toward the reflective layer 5, and the second protective layer and the reflective layer are integrated. In addition, peeling due to thermal stress of laser light due to repeated recording and erasing many times can be prevented. In addition, since the thin film of the second protective 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 becomes uniform. It becomes an amorphous state.
As a result, recording / erasing is improved. Here, although Al is used as the material of the reflective layer 5, the present invention is not limited to this, and materials used for optical information recording media such as W, Bi, Ti, and Ta can be applied. In the disk configuration of the present embodiment,
F1 = 3.43M at outer diameter 130mm, rotation at 1800rpm, linear velocity 8m / sec
The overwrite characteristics of a Hz signal and a signal of f2 = 1.25 MHz were measured. As a result, as the C / N ratio of the recording signal,
55dB or more was obtained, and overwrite erasure rate of 30dB or more was obtained. The cycle characteristics of the overwriting, particularly the results of measuring the characteristics of the bit error rate, 10 ⁶ cycles or more degradation was observed.

[0007]

As described above, according to the present invention, the oxide or nitride of the reflective layer is used for the second protective layer, and the metal or the oxide or nitride composition is moved from the boundary of the recording layer toward the reflective layer. By integrating the second protective layer and the reflective layer by providing a composition gradient so as to obtain a composition, it is possible to prevent the second protective layer and the reflective layer from being peeled off due to thermal stress caused by repetitive recording / erasing, and to perform recording / erasing. Has the effect of improving the repetition characteristics. Further, by adopting a quenching structure in which the second protective layer between the recording layer and the reflective layer is thinned, uniform amorphousization can be achieved, the recording / erasing characteristics are good, and 10 ⁶
An optical recording medium that can be rewritten more than once can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional optical recording medium.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... 1st protective layer, 3 ... recording layer, 4 ...
Second protective layer, 4a: composition gradient layer, 5: reflection layer,
6 ... adhesive 7 ... protection plate

Continuation of the front page (56) References JP-A-64-84453 (JP, A) JP-A-2-177141 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7 / 24 535 G11B 7/24 511 G11B 7/24 538 G11B 7/26 531

Claims (4)

(57) [Claims] 1. A first protective layer on one surface of a transparent substrate,
Irradiation of laser light, etc., absorbs the energy, raises the temperature, melts, rapidly cools, and becomes amorphous. The amorphous state is crystallized by raising the temperature above the crystallization temperature and gradually cooling. sequentially form a recording layer properties, and a second protective layer, and a reflective layer
A formation information rewritable optical recording medium, the oxide of the reflective layer material said second protective layer, or consist of nitrides, oxides towards the reflective layer side from the boundary between the recording layer, Alternatively, the optical recording medium is characterized in that the second protective layer and the reflective layer are integrated by providing a composition gradient from a nitride composition to a metal composition. 2. The method according to claim 1, wherein the thickness of the second protective layer is smaller than that of the first protective layer, and the thickness of the oxide or nitride having a stoichiometric composition is 20 nm or more and 30 nm or less. The optical recording medium according to claim 1, wherein 3. The method according to claim 1, wherein the first protective layer is formed of an oxide of a reflective layer, or
2. The optical recording medium according to claim 1, wherein the optical recording medium is made of nitride . 4. A method for manufacturing the optical recording medium according to claim 1.
The second protective layer is formed of argon and acid.
Sputtering using nitrogen or a mixed gas of argon and nitrogen
After forming by the method, control the amount of oxygen or nitrogen gas
The feature is that the reflective layer is formed after forming the composition gradient.
Manufacturing method of an optical recording medium.