JP3687264B2 - Optical information recording medium and manufacturing method thereof - Google Patents

Description

【００２５】
（表１）から明らかなように、媒体Ａ、媒体Ｂは耐環境試験による剥離やクラックの発生がなく、オーバライト特性も良好であるのに対して、媒体Ｃはオーバライト特性は良好であったが、耐環境試験の結果、剥離が発生し、従来例では耐環境試験による剥離は良好であったが、オーバライト特性ではＣ／Ｎが低下した試験結果が得られた。
【００２６】
つまり、媒体Ａ及び媒体Ｂは、保護層４の記録層５との界面付近の窒素の含有量を少なくすることによって、耐環境性とオーバライト特性がともに良好な光学式情報記録媒体となっている。
【００２７】
なお、上記各実施の形態の説明において、保護層の記録層との界面付近の窒素の含有量を少なくするために、保護層の成膜時の放電電力を該当する部分で大きくしたが、ＡｒガスとＮ₂ガスの混合比を変えてＮ₂ガスの割合を少なくしても良い。また、保護層は、記録層のどちらか一方だけに設けても良いし、両側に設けても良い。さらに、下引層や上引層を保護層で置き換えることもできる。
【００２８】
上記実施の形態の説明では記録層として、Ｇｅ・Ｓｂ・Ｔｅ合金薄膜を用いたが、レーザ光等の照射による熱を利用して情報を記録するものであれば、他の記録層材料を用いた場合でも本発明は有効である。
【００２９】
反射層の材料もＡｕ等、他の金属を用いてもよいし省略することもできる。また、上記実施の形態の説明では、保護層の材料として、Ｇｅ−Ｎを用いたが、記録層を構成する元素の内少なくとも１つの元素、Ｓｉの窒化物を用いても良く、さらに、酸素等のガス元素またはＣｒ、Ａｌ等の非ガス元素等の若干の添加物を加えることも可能である。
【００３０】
【発明の効果】
以上のように本発明は、耐環境性とオーバライト特性がともに優れた光学式情報記録媒体及びその製造方法を提供できる。
【図面の簡単な説明】
【図１】本発明の一実施形態の光学式情報記録媒体の断面図
【図２】本発明の第２の実施形態の光学式情報記録媒体の断面図
【図３】従来の一般的な光学式情報記録媒体の断面図
【符号の説明】
１，１０ 透明基板
２，１１ 案内溝
３，１２ 下引層
４，４’ 保護層
５，１３ 記録層
６，１４ 上引層
７，１５ 反射層
８，１６ 接着剤
９，１７ 保護基板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording medium for recording, reproducing and erasing information by irradiation of a so-called energy beam such as a laser beam, and a manufacturing method thereof.
[0002]
[Prior art]
Optical information recording media are attracting attention as a large-capacity, high-density memory, and development of what is called an erasable type that can be rewritten is underway. As one of the erasable optical information recording media, there is one that uses a thin film that changes phase between an amorphous state and a crystalline state as a recording layer, and records and erases information by thermal energy by laser light irradiation.
[0003]
As the phase change material for the recording layer, an alloy film containing Ge, Sb, Te, In or the like as a main component is generally known.
[0004]
Information recording is generally performed by forming marks by partially amorphizing the recording layer, and erasing is often performed by crystallization of the amorphous marks. Amorphization is performed by heating the recording layer to the melting point or higher and then cooling it at a speed equal to or higher than a certain value. Crystallization is performed by heating the recording layer to a temperature not lower than the crystallization temperature and not higher than the melting point.
[0005]
In general, dielectric layers are provided above and below the recording layer. The purpose of this dielectric layer is to protect the substrate from the heat of the recording layer that instantaneously rises above the melting point, and to protect the substrate from deformation and breakage of the recording layer. This is an optical action that obtains sufficient signal intensity during reproduction of recorded information due to the optical interference effect, and third, a thermal action that realizes a cooling rate suitable for forming an amorphous mark having a good shape during recording. . Therefore, characteristics required for this dielectric material are sufficient heat resistance, a large refractive index, an appropriate thermal conductivity, and the like. As materials satisfying these conditions, for example, many ZnS—SiO ₂ and Si ₃ N ₄ have been proposed.
[0006]
FIG. 3 is a cross-sectional view of an example of a conventional erasable optical information recording medium, which is made of ZnS—SiO ₂ on a disc-like transparent substrate 10 having a central hole and provided with a guide groove 11 and having a film thickness of about 120 nm substrate-side dielectric layer (hereinafter referred to as undercoat layer) 12, Ge · Sb · Te alloy thin film, about 20 nm thick recording layer 13, ZnS—SiO ₂ , reflective about 30 nm thick A layer-side dielectric layer (hereinafter referred to as an overcoat layer) 14, an Al alloy, a reflective layer 15 having a thickness of about 150 nm is formed, and a protective substrate 17 is provided thereon with an adhesive 16 is there.
[0007]
Since the Ge.Sb.Te alloy has a very high crystallization speed, it can be amorphized and crystallized simply by modulating the intensity of a single laser beam. Therefore, this optical information medium can be rewritten by a single laser beam generally called “overwrite”. At this time, the film thickness of the undercoat layer 12 and the overcoat layer 14 is such that sufficient signal intensity can be obtained during reproduction due to the optical interference effect, and sufficient cooling of the recording layer to form an amorphous mark having a good shape during recording. Designed for speed.
[0008]
In such an optical information recording medium, since the recording layer is generally in an amorphous state at the time of formation, it needs to be in a crystalline state before use. This process is called initialization. This initialization is generally performed by irradiating an Ar laser formed with a spot diameter of several tens of μm while rotating the optical information recording medium to crystallize the recording layer over the entire surface.
[0009]
[Problems to be solved by the invention]
However, when recording and erasing is repeated on the conventional optical information recording medium shown in FIG. 3, there is a problem that the signal amplitude at the time of reproduction gradually decreases and an error may occur in reading information. As a cause of this, it is conceivable that interdiffusion occurs at the interface between the recording layer and the undercoat layer or the interface between the recording layer and the overcoat layer and the composition of the recording layer changes.
[0010]
On the other hand, when a nitride such as Si ₃ N ₄ is used for the undercoat layer and the overcoat layer, it is initialized and maintained at a high temperature and high humidity such as 90 ° C. and 80% RH from the room temperature environment. When repeated charging and unloading into the tank, there was a problem that partial peeling or cracking of the film occurred. This is considered to be caused by expansion and contraction due to initialization or environmental change because the adhesive force with the recording layer is weak.
[0011]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional problems, and to provide an optical information recording medium having good repeated erasing performance and being resistant to environmental changes.
[0012]
In order to achieve this object, the optical information recording medium of the present invention is provided with a protective layer, which is a thin film mainly composed of Ge—N, on at least one side of the recording layer. The nitrogen content in the vicinity of the interface with at least one is made lower than the average nitrogen content in the protective layer .
[0013]
In another optical information recording medium of the present invention, a protective layer, which is a thin film mainly composed of Ge—N, is provided on at least one side of the recording layer, and an interface between at least one of the protective layer and the recording layer A structure in which the nitrogen content in the vicinity changes continuously, or a plurality of thin films with different nitrogen contents, and the content of nitrogen in the protective layer in contact with the recording layer is reduced. Yes .
[0014]
On the other hand, in the method for producing an optical information recording medium according to the present invention, a protective layer, which is a thin film containing Ge—N as a main component, is formed on at least one side of the recording layer, the main component of the protective layer or a nitride thereof. Using a target, a film is formed by reactive sputtering in a mixed gas of a rare gas and a gas having a nitrogen component, and in at least one of the recording layers, the sputtering power is temporarily increased near the interface with the recording layer. Or temporarily reducing the proportion of the gas having a nitrogen component in the mixed gas .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an optical information recording medium and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
[0016]
(Embodiment 1)
FIG. 1 is a cross-sectional view of an optical information recording medium according to an embodiment of the optical information recording medium of the present invention. The optical information recording medium of the present embodiment has a center hole, a disk-shaped polycarbonate transparent substrate 1 having a spiral guide groove 2 having a groove width of about 0.7 μm and a pitch of about 1.5 μm. An undercoat layer 3 containing ZnS—SiO _{2 and} having a thickness of about 100 nm, a protective layer 4 containing Ge—N and having a thickness of about 20 nm, a recording layer 5 made of a Ge · Sb · Te alloy thin film and having a thickness of about 20 nm, ZnS— An overcoat layer 6 containing SiO _{2 and} having a thickness of about 30 nm, and a reflective layer 7 made of Al alloy and having a thickness of about 150 nm are formed by sputtering, and a protective substrate 9 is provided thereon with an adhesive 8. is there.
[0017]
The undercoating layer 3 and the overcoating layer 6 are formed by sputtering using Ar gas with a sintered body made of a mixture of ZnS and SiO ₂ as a target. At this time, the target had a diameter of 60 mm and a thickness of 6 mm, and the sputtering was high-frequency magnetron sputtering with a pressure of 2 mTorr and a discharge power of 500 W.
[0018]
The recording layer 5 was formed in the same manner as the undercoat layer 3 using a sintered body of Ge, Sb, and Te having a predetermined composition ratio as a target.
[0019]
The protective layer 4 is formed by using Ge as a target, first introducing Ar gas and N ₂ gas into the film forming apparatus at a ratio of 1: 1, and starting film formation by high-frequency magnetron sputtering with a pressure of 10 mTorr and a discharge power of 500 W, While the film formation was continued when the film thickness was about 15 nm, the discharge power was switched to 1 kW to form the remaining about 5 nm.
[0020]
As a result of analysis such as Auger electron spectroscopy (AES), the portion of the protective layer 4 formed with a discharge power of 500 W has a nitrogen content of about 50%, and the portion formed with a discharge power of 1 kW has a nitrogen content of about 50%. 30%. The optical information recording medium of Embodiment 1 is referred to as medium A.
[0021]
(Embodiment 2)
FIG. 2 is a cross-sectional view of an optical information recording medium in another embodiment of the optical information recording medium of the present invention. As in the first embodiment, the optical information recording medium of the present embodiment has a center hole, and has a disk-like shape having a spiral guide groove 2 having a groove width of about 0.7 μm and a pitch of about 1.5 μm. On a polycarbonate transparent substrate 1, an undercoat layer 3 containing ZnS—SiO _{2 and} having a thickness of about 100 nm, a protective layer 4 ′ containing Ge—N and having a thickness of about 20 nm, and a Ge · Sb · Te alloy thin film. A recording layer 5 having a thickness of about 20 nm, an overcoat layer 6 containing ZnS—SiO _{2 and} having a thickness of about 30 nm, and a reflective layer 7 made of an Al alloy and having a thickness of about 150 nm are formed by sputtering, and an adhesive 8 is formed thereon. The protective layer 4 ′ is provided with a protective layer 4 ′. Ge is used as a target, Ar gas and N ₂ gas are first introduced into the film forming apparatus at a ratio of 1: 1, and the pressure is 10 mTorr. High frequency magnetron spattering with 500W power After the film formation was started, the film formation was temporarily stopped by the shutter when the first layer 4-1 of about 15 nm was formed, and then the second layer 4-2 of about 5 nm was formed with a discharge power of 1 kW. It is a thing. This optical information recording medium of Embodiment 2 is referred to as medium B.
[0022]
For comparison, the protective layer 4 is entirely formed at a discharge power of 500 W with the same structure as that of the medium A, that is, the nitrogen content is the same as that in the central portion even near the interface of the protective layer 4 with the recording layer 5. A medium C, which differs only in that it is about 50%, was created, the medium A, medium B, medium C and the conventional medium shown in FIG. 3 were initialized, and then an environmental resistance test and an overwrite characteristic test were performed. The results are shown in (Table 1).
[0023]
However, in the environmental resistance test, pass / fail was determined by the presence or absence of peeling and cracks after leaving in a constant temperature and humidity chamber maintained at 90 ° C. and 80% RH for 500 hours. In addition, the overwrite characteristic test is performed by rotating an optical information medium of A to C and the conventional example, an optical system having a laser beam having a wavelength of 680 nm and an objective lens having a numerical aperture of 0.6 at a linear velocity of 6 m / sec. 3T signal C / N ratio when the 3T signal and 11T signal of the shortest recording mark 3T having a mark length of 0.6 μm and a bit length of 0.4 μm are overwritten alternately by PWM recording. Is determined by the number of overwriting times of 50 dB or more.
[0024]
[Table 1]

[0025]
As is clear from Table 1, medium A and medium B are free from peeling and cracking due to the environmental resistance test, and have good overwrite characteristics, while medium C has good overwrite characteristics. However, as a result of the environmental resistance test, peeling occurred. In the conventional example, the peeling by the environmental resistance test was good, but in the overwrite characteristics, the test result in which C / N was reduced was obtained.
[0026]
That is, the medium A and the medium B are optical information recording media having both good environmental resistance and overwriting characteristics by reducing the nitrogen content in the vicinity of the interface between the protective layer 4 and the recording layer 5. Yes.
[0027]
In the description of each of the above embodiments, in order to reduce the nitrogen content in the vicinity of the interface between the protective layer and the recording layer, the discharge power at the time of forming the protective layer was increased at the corresponding part. The ratio of N ₂ gas may be reduced by changing the mixing ratio of gas and N ₂ gas. The protective layer may be provided on only one of the recording layers or on both sides. Furthermore, the undercoat layer and the overcoat layer can be replaced with a protective layer.
[0028]
In the description of the above embodiment, a Ge / Sb / Te alloy thin film is used as the recording layer. However, other recording layer materials may be used as long as information is recorded using heat by irradiation with laser light or the like. Even in such a case, the present invention is effective.
[0029]
The material of the reflective layer may be other metal such as Au or may be omitted. In the description of the above embodiment, Ge—N is used as the material for the protective layer. However, at least one of the elements constituting the recording layer, Si nitride, may be used, and oxygen It is also possible to add some additives such as gas elements such as Cr or non-gas elements such as Cr and Al.
[0030]
【The invention's effect】
As described above, the present invention can provide an optical information recording medium excellent in both environmental resistance and overwrite characteristics, and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a sectional view of an optical information recording medium according to an embodiment of the present invention. FIG. 2 is a sectional view of an optical information recording medium according to a second embodiment of the present invention. Sectional view of formula information recording medium [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,10 Transparent substrate 2,11 Guide groove 3,12 Undercoat layer 4,4 'Protective layer 5,13 Recording layer 6,14 Overcoat layer 7,15 Reflective layer 8,16 Adhesive 9,17 Protective substrate

Claims (5)

A recording layer made of a phase change material mainly composed of Ge, Sb, and Te, which causes a state change optically detectable at least by irradiation of an energy beam on a transparent substrate, and at least one of the recording layers An optical information recording medium provided with a protective layer that is a thin film mainly composed of Ge-N on the side, wherein the nitrogen content in the vicinity of the interface between the recording layer and at least one of the protective layers is An optical information recording medium characterized by being less than the average content of nitrogen in the protective layer.   2. The optical information recording medium according to claim 1, wherein the nitrogen content in the vicinity of the interface between the recording layer and at least one protective layer in contact with the recording layer continuously changes.   The optical information recording medium according to claim 1, wherein the protective layer is composed of a plurality of thin films having different nitrogen contents. A recording layer made of a phase change material mainly composed of Ge, Sb, and Te, which causes a state change optically detectable at least by irradiation of an energy beam on a transparent substrate, and at least one of the recording layers A method for producing an optical information recording medium, wherein a protective layer, which is a thin film mainly composed of Ge—N, is formed on a side by sputtering, wherein at least one of the protective layers, Using the target made of nitride, forming a film by reactive sputtering in a mixed gas of a rare gas and a gas having a nitrogen component, and temporarily increasing the sputtering power near the interface with the recording layer A method for manufacturing an optical information recording medium. A recording layer made of a phase change material mainly composed of Ge, Sb, and Te, which causes a state change optically detectable at least by irradiation of an energy beam on a transparent substrate, and at least one of the recording layers A method for producing an optical information recording medium, wherein a protective layer, which is a thin film mainly composed of Ge—N, is formed on a side by sputtering, wherein at least one of the protective layers, The nitride target is used to form a film by reactive sputtering in a mixed gas of a rare gas and a gas having a nitrogen component, and temporarily has a nitrogen component in the mixed gas near the interface with the recording layer. A method for producing an optical information recording medium, wherein the ratio of gas is reduced.

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