JPH1016393A - Phase change type optical data recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase change type optical data recording medium drastically enhanced in the repeating characteristics of recording and erasure. SOLUTION: A protective layer 2 with a thickness of 100nm containing ZnS and SiO2 in a mixing ratio being a mol ratio (ZnS:SiO2 ) of 8:2, a recording membrane 3 with a thickness of 25nm composed of Ge2 Sb2 Te5 being a phase change material, a protective layer 4 with a thickness of 30nm containing ZnS and SiO2 in a mixing ratio being a mol ratio (ZnS:SiO2 ) of 8:2 and a reflecting layer 5 with a thickness of 20nm composed of Au are successively formed on a glass substrate with a thickness of 0.2μm by a magnetron sputtering apparatus. In the process forming the recording membrane 3, the concn. of nitrogen gas in a film forming atmosphere gas during a period growing a membrane (surface layer part 3a) with a thickness of 2nm from the start of the process is set to 0.7mTorr and, after this period, the concn, of nitrogen gas in the film forming atmosphere gas up to the completion of the film forming process is set to 5μTorr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical information recording medium used for an information recording / reproducing apparatus using a laser beam and a method for manufacturing the same.

[0002]

2. Description of the Related Art As an optical information recording medium capable of recording / reproducing and erasing a signal, a phase change type optical disk using a chalcogenide as a recording thin film material is known. In such a phase-change type optical disk, signal recording is generally performed by setting the recording thin film material in a crystalline state to an unrecorded state, irradiating a laser beam to melt and rapidly cool the recording thin film material to an amorphous state. Is made. On the other hand, signal erasure is performed by irradiating a laser beam having a lower power than at the time of signal recording to raise the temperature of the recording thin film and return it to a crystalline state again. The complex refractive index consisting of the refractive index n and the extinction coefficient k differs between the crystalline state and the amorphous state of the recording thin film material, and the signal is reproduced by utilizing the difference in the optical characteristics (reflectance or transmittance) caused by this. Is performed.

[0003] As a recording thin film material of the optical disk,
For example, a compound mainly containing Te, In, Sb, Se or the like which changes phase between an amorphous and a crystal, a substance which reversibly changes phase between two different types of crystal structures, and the like are used. Examples of the material of the protective layer include Al ₂ O ₃ ,
SiO ₂ , SiO, Ta ₂ O ₅ , MoO ₃ , WO ₃ , Zn
S, ZrO ₂ , AlN, BN, SiN _x , TiN, Zr
One or more selected from various dielectric materials such as N, PbF ₂ , and MgF ₂ are used.

One of the advantages of the information recording method using a phase change recording medium such as the phase change type optical disk is that an information signal can be overwritten (overwritten) by using only a single laser beam as recording means. It is in. That is, when the laser output is modulated between two levels of a recording level and an erasing level in accordance with the information signal and irradiated onto a recorded information track, a new signal can be recorded while erasing the existing information signal. (This is described in detail, for example, in JP-A-56-145530.) Taking advantage of such advantages, the phase-change optical disk is used as a document file, an image file, or a data file.

[0005]

By the way, from the viewpoint of improving the repetition characteristics of recording / erasing in a phase change type optical information recording medium such as the phase change type optical disk, the film quality of the recording thin film and the protective layer has been conventionally known. There have been many suggestions for improving. For example, Japanese Patent Application Laid-Open No. 2-113380 discloses that by providing a recording thin film formed at an appropriate partial pressure of nitrogen, good cycle characteristics (repetition characteristics of recording / erasing) can be obtained. Also, Japanese Patent Laid-Open No. Hei 3
JP-A-232133 discloses that a good cycle characteristic (repeated recording / erasing characteristic) can be obtained by providing a protective layer formed at an appropriate partial pressure of nitrogen. However, in recent years, there has been a strong demand for further improvement of the recording / erasing repetition characteristics of the phase-change optical information recording medium, and the recording / erasing repetition characteristics of the optical information recording medium according to the conventional proposal have been improved to a satisfactory level. I couldn't let it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a phase-change optical information recording medium in which repetition characteristics of recording and erasing are dramatically improved, and a method of manufacturing the same. I do.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and found that repetition of recording / erasing on a rewritable phase-change optical information recording medium such as a phase-change optical disc is repeated. One of the causes of the deterioration of the reproduction signal quality due to the interdiffusion occurring at the interface between the recording thin film and the protective layer during laser irradiation, and conceived a phase-change optical information recording medium of the present invention having the following configuration. I came to.

That is, the first phase-change type optical information recording medium of the present invention contains a base material and nitrogen provided as a constituent element on the base material, and the optical information medium before and after laser beam irradiation. In a phase-change optical information recording medium comprising a recording thin film whose characteristics are reversibly changed, and a protective layer formed on one surface or both surfaces of the recording thin film, the recording thin film is composed of The element having the largest rate of concentration change in the thickness direction of the thin film is nitrogen, and the surface layer portion including the surface forming the interface with the protective layer substantially prevents interdiffusion between the recording thin film and the protective layer. It is characterized by having a high nitrogen concentration necessary for suppression. With such a configuration, the surface layer having a high nitrogen concentration of the recording thin film functions as a barrier layer that suppresses interdiffusion between the recording thin film and the protective layer. The synergistic effect of the recording thin film itself with the film quality improvement effect of the recording
The repetition characteristics of erasure will be dramatically improved. In addition, since the surface layer having a high nitrogen concentration of the recording thin film can be formed during the process of forming the recording thin film, a phase-change optical information recording medium having a configuration in which a barrier layer is provided separately from the conventional recording thin film and the protective layer. As described above, there is no need to separately add a step of forming a barrier layer other than the step of forming a recording thin film and a protective layer.
The manufacturing cost of the recording medium can be reduced.

In the first phase-change type optical information recording medium of the present invention, the average nitrogen concentration of the portion having a thickness of 2 nm from the surface forming the interface with the protective layer of the recording thin film has the thickness of 2 nm. It is preferably at least three times the average nitrogen concentration of the parts other than the part. With such a configuration, the effect of suppressing the mutual diffusion between the recording thin film and the protective layer by the surface layer portion of the recording thin film can be reliably obtained.

A second phase-change optical information recording medium of the present invention is a recording medium comprising: a base material; and a recording thin film whose optical characteristics are reversibly changed before and after irradiation with a laser beam provided on the base material. And a protective layer formed on one surface or on both surfaces of the recording thin film and containing nitrogen as a constituent element thereof, wherein the protective layer comprises the constituent element Is the element whose concentration change in the thickness direction of the layer is the largest, and the surface layer portion including the surface forming the interface with the recording thin film is substantially interdiffused between the recording thin film and the protective layer. Characterized by having a high nitrogen concentration necessary for suppressing the occurrence of nitrogen. With such a configuration, the surface portion of the protective layer having a high nitrogen concentration functions as a barrier layer that suppresses interdiffusion between the recording thin film and the protective layer, and the surface layer portion suppresses interdiffusion and contains nitrogen in the protective layer. The effect of improving the film quality of the protective layer itself due to the synergistic effect dramatically improves the repetition characteristics of recording / erasing. Also,
Since the surface layer having a high nitrogen concentration of the protective layer can be formed during the process of forming the protective layer, as in a phase-change optical information recording medium having a configuration in which a barrier layer is provided separately from a conventional recording thin film and a protective layer. In addition, there is no need to separately add a step of forming a barrier layer in addition to the step of forming a recording thin film and a protective layer, so that the manufacturing cost of a recording medium can be reduced.

In the second phase-change type optical information recording medium of the present invention, the average nitrogen concentration in the portion having a thickness of 2 nm from the surface forming the interface with the recording thin film of the protective layer has the thickness of 2 nm. It is preferably at least three times the average nitrogen concentration of the parts other than the part. With such a configuration, the effect of suppressing mutual diffusion between the recording thin film and the protective layer by the surface layer portion of the protective layer can be reliably obtained.

A first method for manufacturing a phase-change optical information recording medium according to the present invention is a method for manufacturing the first phase-change optical information recording medium according to the first aspect of the present invention. The nitrogen gas (N ₂ ) concentration in the film formation atmosphere gas during the period of forming the surface layer including the surface forming the surface is determined by the average nitrogen in the film formation atmosphere gas during the period of forming the film other than the surface layer. It is characterized in that the recording thin film is formed at a concentration higher than the gas (N ₂ ) concentration. With such a configuration, the above-described first phase-change optical information recording medium of the present invention can be rationally and stably manufactured.

Further, a second method of manufacturing a phase change type optical information recording medium of the present invention is a method of manufacturing the above-mentioned first phase change type optical information recording medium of the present invention, wherein The average film forming rate during the period in which the surface layer portion including the surface forming the interface forming the film is formed is made smaller than the average film forming rate in the period during which the portions other than the surface layer portion are formed. It is characterized by forming a film. With such a configuration, the above-described first phase-change optical information recording medium of the present invention can be rationally and stably manufactured.

Further, a third method of manufacturing a phase change type optical information recording medium of the present invention is a method of manufacturing the second phase change type optical information recording medium of the present invention described above, wherein The average nitrogen gas (N ₂ ) concentration in the film formation atmosphere gas during the film formation of the surface layer portion including the surface forming the interface with the surface of the film is determined by calculating the average nitrogen gas (N ₂ ) concentration The protective layer is formed at a concentration higher than the average nitrogen gas (N ₂ ) concentration. With such a configuration,
The above-mentioned second phase-change type optical information recording medium of the present invention can be manufactured reasonably and stably.

Further, a fourth method of manufacturing a phase change type optical information recording medium of the present invention is a method of manufacturing the second phase change type optical information recording medium of the present invention, wherein the recording thin film and The protective layer is formed by setting the average film forming rate during the period of forming the surface layer portion including the surface forming the interface of the surface to be smaller than the average film forming rate during the period of forming the portion other than the surface layer portion. It is characterized by the following. With such a configuration, the above-described second phase-change optical information recording medium of the present invention can be manufactured reasonably and stably.

[0016]

FIG. 1 is a cross-sectional view showing the structure of one embodiment of a phase change type optical information recording medium of the present invention. In FIG. 1, reference numeral 1 denotes a base material; Is a recording thin film, 3
Reference numerals a and 3b denote surface layer portions of the recording thin film 3, 5 denotes a reflective layer, 6 denotes an adhesive layer, 7 denotes a protective substrate, and 8 denotes a laser beam for recording / erasing and reproducing.

The substrate 1 is a plate or film having a smooth surface, and is made of a resin such as PMMA (polymethyl methacrylate) or polycarbonate, or a transparent material such as glass. For optical disks,
The base material 8 is plate-shaped, and its surface 1a is covered with a spiral or concentric track for guiding a laser beam. When the substrate 1 is a plate-like body, its thickness is not particularly limited, but is generally 0.6 to 1.2 mm.

The recording thin film 3 contains a known phase change material and a nitrogen atom, which reversibly changes phase from a crystalline state to an amorphous state or from an amorphous state to a crystalline state by irradiation heat of a laser beam. It is composed. As the phase change material, a chalcogen compound such as Te or Se, which contains chalcogen (oxygen group element) as a main component, and a compound containing In as a main component are generally used. Specific examples of these chalcogen compounds and compounds containing In include Te-Sb-Ge,
Te-Ge, Te-Ge-Sn, Te-Ge-Sn-A
u, Sb-Te, Sb-Se-Te, In-Te, In
-Se, In-Se-Tl, In-Sb, In-Sb-
Se, In-Se-Te, and the like. The thickness of the recording thin film 3 is not particularly limited, but is generally 5 to 50 nm. In the recording thin film 3, a surface layer 3 a having a predetermined thickness including the lower surface (the surface in contact with the protective layer 2).
And the average nitrogen (N) concentration (content of nitrogen atoms per unit volume) in at least one of the surface layer portions 3 b having a predetermined thickness including the upper surface (the surface in contact with the protective layer 4)
It is larger than that in other portions of the recording thin film 3 other than the surface layer 3a (surface layer 3b). The average nitrogen concentration in other portions of the recording thin film 3 other than the surface layer 3a (surface layer 3b) is not particularly limited, but may be 0.1 to 3
It is often 0 atomic%. Surface layer 3a (surface layer 3
The average nitrogen concentration and thickness in b) are appropriately determined in consideration of the constituent material and thickness of the recording thin film 3, the constituent material and thickness of the protective layer 2 (protective layer 4), and the like. As is apparent, the thickness of the surface layer 3a (surface layer 3b) is 1
It is preferable that the average nitrogen concentration of the surface layer 3a (surface layer 3b) be 2 nm or more. For example, the average nitrogen concentration of the other portion of the recording thin film 3 other than the surface layer 3a (surface layer 3b) is obtained. If it is three times or more, a barrier function for suppressing the mutual diffusion between the recording thin film and the protective layer is surely developed.

The protective layers 2 and 4 are made of a material that is physically and chemically stable, has a higher melting point and softening temperature than the melting point of the phase change material constituting the recording thin film 3 and does not form a solid solution with the phase change material. Become. Such materials include, for example, Al ₂ O ₃ , Si
O _x , Ta ₂ O ₅ , MoO ₃ , WO ₃ , ZnS, ZrO
₂ , AlN _x , BN, SiN _x , TiN, ZrN, Pb
Various dielectric substances such as F ₂ and MgF ₂ may be mentioned, and one or more selected from them may be used. Although the thickness of the protective layers 2 and 4 is not particularly limited,
Generally, it is set to 00 nm. In addition, such protective layers 2 and 4 do not necessarily need to have a dielectric property or transparency,
For example, Zn which has a light absorbing property for visible light and infrared light
It may be formed of Te or the like. Further, only one of the protective layer 2 and the protective layer 4 may be provided. When both the protective layer 2 and the protective layer 4 are provided, they may be formed of the same material or different materials. There is an advantage that the degree of freedom is increased.

The reflection layer 5 is made of Au, Al, Ag, Ni, F
It is made of metal elements such as e and Cr and alloys thereof. In addition,
The reflection layer 5 is a layer that functions to enhance the light absorption efficiency of the recording thin film, and is not an essential layer. Although the thickness of the reflective layer 5 is not particularly limited, it is generally 10 to 200 nm.

The protective substrate 7 is formed by spin-coating a resin,
It is formed by bonding a resin or glass plate or film used as the base material 1 or a metal plate or film using an adhesive 6.

The recording thin film 3 and the protective layers 2 and 4 are formed by sputtering, electron beam evaporation, ion plating,
It is formed using a known thin film manufacturing technique in vacuum such as a CVD method or a laser sputtering method, but is most commonly formed by a sputtering method.

Although the recording medium of FIG. 1 is a recording medium having a single-layered recording thin film, the present invention uses two sets of the recording medium of FIG. The recording medium may be structured such that recording, erasing, and reproduction can be performed from both sides by bonding the substrate 7 with the substrate 7 inside.

In the recording medium of FIG. 1, the recording thin film 3 contains nitrogen. In the present invention, as shown in FIG. 2, at least one of the protective layer 2 and the protective layer 4 is made of nitrogen. And the average nitrogen concentration of the surface layer portion 2a (surface layer portion 4a) including the surface in contact with the recording thin film 3 is larger than that of the other portions other than the surface layer portion 2a (surface layer portion 4a). You may make it. In this case, the average nitrogen concentration in the portion other than the surface layer portion 2a (surface layer portion 4a) of the protective layer 2 (protective layer 4), that is, in the central portion is not particularly limited, but is 0.1 to 30 atomic.
%. The average nitrogen concentration and thickness of the surface portion 2a (surface portion 4a) are appropriately determined in consideration of the constituent material and thickness of the recording thin film 3, the constituent materials and thickness of the protective layers 2 and 4, and the like, and will be described later. As is clear from the examples, the thickness of the surface layer portion 2a (surface layer portion 4a) is preferably set to 1 nm or more.
If the average nitrogen concentration in the (surface layer portion 4a) is three times or more the average nitrogen concentration in the other portions of the protective layers 2 and 4 other than the surface layer portion 2a (surface layer portion 4a), interdiffusion between the recording thin film and the protective layer is prevented. The barrier function that suppresses the phenomena is surely developed.

As described above, in the phase-change optical information recording medium of the present invention, nitrogen is contained in the recording thin film 3 or the protective layer 2 (4), and the recording thin film 3 or the protective layer 2 (4) is filled with nitrogen. By making the average nitrogen concentration in the surface layer portion including the surface serving as the interface of the surface layer larger than the average nitrogen concentration in the portions other than the surface layer portion, the surface layer portion becomes the recording thin film 3 and the protective layer 2 (4). It functions as a barrier layer that substantially suppresses interdiffusion that occurs between them.

The phase-change type optical information recording medium of the present invention can be rationally and stably manufactured by the first or second manufacturing method described below. That is, in the first method, when the nitrogen concentration in the film forming atmosphere gas is increased in the film forming step of the recording thin film 3 or the protective layer 2 (4), the amount of nitrogen taken in the film increases. Alternatively, the average nitrogen concentration in the film formation atmosphere gas during a certain period after the start of film formation in the film formation step of the protective layer 2 (4) or during a certain period before the end of film formation is calculated as the average nitrogen concentration in the film formation atmosphere gas during another period. This is a method of making the nitrogen concentration larger than the nitrogen concentration. Further, in the second method, when the film forming rate is reduced in the film forming step of the recording thin film 3 or the protective layer 2 (4), the amount of nitrogen taken in the film increases. 4)
In this method, the average film forming speed in a certain period after the start of film formation or in a certain period before the end of film forming in the film forming step is made smaller than the average film forming speed in other periods.

In the case where the surface layer 3a (3b) serving as a substantial barrier layer is formed on the recording thin film 3 by the first method,
In order to improve the barrier function of the surface layer portion 3a (3b), it is necessary to perform recording in the film forming process of the recording thin film 3 so that the surface layer portion 3a (3b) exhibits a stable barrier function. The average nitrogen gas (N ₂ ) concentration in the film formation atmosphere gas during a period during which the surface layer portion 3a (3b) of the thin film 3 is formed, that is, during a certain period immediately after the start of the process or a certain period immediately before the end of the process is set to another period. It is preferable to set the concentration to be at least three times the average nitrogen gas (N ₂ ) concentration in the film formation atmosphere gas in the above.
In the case where the surface layer 2a (4a) serving as a barrier layer is formed on the surface layer 4, the surface layer 2a (4a) must have a stable barrier function in order to further improve the barrier function of the surface layer 2a (4a). In order to exert the effect, the surface layer 2a (4a) of the protective layers 2 and 4 is formed during the process of forming the protective layers 2 and 4, that is, a certain period after the start of the process or before the process is completed. It is preferable that the average nitrogen concentration in the film formation atmosphere gas during a certain period be at least three times the average nitrogen gas (N ₂ ) concentration in the film formation atmosphere gas during another period.

In the case where the surface portion 3a (3b) serving as a barrier layer is formed on the recording thin film 3 by the second method, the barrier function of the surface portion 3a (3b) is required to be more excellent ( In order for the surface portion 3a (3b) to exhibit a stable barrier function, a period during which the surface portion 3a (3b) of the recording thin film 3 is formed in the film forming process of the recording thin film 3, that is, after the start of the process. It is preferable that the average film forming rate during a certain period of time or a certain period before the end of the process is equal to or less than one third of the average film forming speed during the other period. When the surface layer 2a (4a) serving as a barrier layer is formed in 4), the surface layer 2a is formed.
In order to make the barrier function of (4a) more excellent (in order for the surface layer portion 2a (4a) to exhibit a stable barrier function, the protection in the film forming step of the protective layer 2 (4) is required. The period during which the surface layer portion 2a (4a) of the layer 2 (4) is formed, that is, the average film forming speed in a certain period after the start of the process or a certain period before the end of the process is reduced to the average film forming speed in another period. It is preferable to make it one third or less.

[0029]

【Example】

Example 1 The effect of improving the repetitive recording characteristics by providing a surface layer having a high nitrogen concentration on the recording layer was examined for a phase change type optical disk having the layer configuration shown in FIG.

The basic structure of the optical disk was as follows. The substrate was a glass substrate having a thickness of 1.2 mm, and the phase change material constituting the recording thin film was Ge ₂ Sb ₂ Te ₅ . This Ge ₂ Sb ₂ Te ₅ is conventionally known as a constituent material of a recording thin film of an optical information recording medium having excellent recording / erasing characteristics and repetition characteristics (Japanese Patent Laid-Open No. 62-209).
742). The thickness of the recording thin film was 25 nm. For the recording thin film, the molar ratio of ZnS to SiO ₂ (ZnS: SiO
₂ ) sandwiched by protective layers comprising a mixture of 8: 2. The thickness of the protective layer on the substrate side was 100 nm, and the thickness of the protective layer (the protective layer provided on the upper surface of the recording thin film) on the protective substrate side was 30 nm. The reflection layer was formed of gold (Au) and had a thickness of 20 nm.

Each layer was formed by a magnetron sputtering method. In the step of forming layers other than the recording thin film, the film forming atmosphere gas was only Ar gas and the pressure was 3 mTorr.
On the other hand, in the recording thin film forming process, the film forming atmosphere gas is a mixed gas of Ar gas and N ₂ gas, and the partial pressure of Ar gas is 3 mT.
The pressure was fixed at orr, and the partial pressure of N ₂ gas was changed to a plurality of different values. The film formation power was set to 100 W in any of the layer forming steps. The diameter of the sputter target was 100 mm in any layer forming process, and the distance between the sputter target and the substrate was 150 mm.

FIG. 3 is a schematic diagram showing the structure of a magnetron sputtering apparatus used in the step of forming each layer. Sputter target 1 as a cathode in vacuum chamber 9
0 and the substrate holder 11 are arranged at positions facing each other. As the sputter target 10, three different types of sputter targets for a protective layer, a recording thin film, and a reflective layer are prepared, and each layer can be sputter-deposited individually. The inside of the chamber 9 is evacuated by the exhaust system 12 and at the same time, a desired film forming atmosphere gas is introduced by the gas introduction pipes 13 and 14. The gas pressure at the time of film formation is controlled by the mass flow controller 1 to which gas introduction pipes 13 and 14 are attached.
5 and 16. The film is formed by colliding the ionized introduced gas with a cathode sputtering target.

FIG. 4 is a diagram schematically showing a configuration of an evaluation apparatus used for a repeated test of recording and erasing of the manufactured optical disk. In the figure, 30 is a laser irradiation source, 31 is an objective lens, 32 and 32 are photodetectors, 34 is a motor, and 35 is an optical disk. Using such an evaluation device, a motor 34 outputs a laser beam (wavelength: 780).
nm) and the optical disk 35 is rotated so that the relative speed becomes 14 m / sec, and the shortest mark period is 1.1 μm.
At m, random data was overwritten (overwritten) by 2-7 modulation mark position recording, and the change in BER (Bit Error Rate) with the number of repeated recordings was measured. The laser power for performing the repetitive recording here was determined as follows. That is, overwrite recording is performed by irradiating the recording medium with a laser having two values of peak power and bias power as shown in FIG. Here, the peak power and the bias power are set to 0.2 m.
The BER change was measured at intervals of W, and the minimum power among the recording / erasing powers at which the BER value after repeating 100 times was 1 × 10 ⁻⁵ or less was set as the lower limit power. The repetitive recording characteristics were evaluated by repeatedly recording with a recording / erasing power 15% higher than the lower limit power, and measuring the number of repetitions when the BER became larger than 1 × 10 ⁻⁵ .

Table 1 shows the number of repetitions of recording / erasing of an optical disk having a recording thin film formed at a constant nitrogen (N ₂ ) partial pressure in a film forming atmosphere gas from the start of the process to the end of the process. Is shown.

[0035]

[Table 1]

From Table 1, it can be seen that, when an optical disk is formed using a recording thin film formed with a constant N ₂ partial pressure in the film formation atmosphere gas from the start of the film formation process to the end of the process, the formation of the recording thin film In the film forming atmosphere gas in the film forming process, there is a preferable N ₂ partial pressure for improving the recording / erasing repetition characteristics of the optical disk, and it is found that this is 50 μTorr here. It is disclosed in Japanese Patent Application Laid-Open No. 2-113380, for example, that an optical disk using a recording thin film formed at such a moderate N ₂ partial pressure exhibits good cycle characteristics. However, the preferable N ₂ partial pressure strongly depends on the film forming conditions (the film forming apparatus to be used), and may show different values under the different film forming conditions (film forming apparatus).

Column A in Table 2 below shows various changes in the partial pressure of N ₂ in the film forming atmosphere gas during the period from the start of the film forming process to the growth of a 2 nm thick film (the first 2 nm film). The N ₂ partial pressure in the film formation atmosphere gas after the above period was set to the preferable N ₂ obtained from the experimental results shown in Table 1 above.
It shows the number of repetitions of recording / erasing of an optical disk having a recording thin film formed by setting the partial pressure (50 μTorr). From the stage A in Table 2, the N ₂ partial pressure in the film formation atmosphere gas during the period in which the film having the predetermined thickness grows at the start of the film formation step is compared with that in the film formation atmosphere gas after the predetermined period. It can be seen that the optical disc using the recording thin film formed by increasing the film thickness has further improved recording / erasing repetition characteristics than the optical disc shown in Table 1.

Column B in Table 2 below shows the N ₂ partial pressure in the film formation atmosphere gas during the period from the start of the film formation process to the growth of a film having a thickness of 2 to 5 nm (the first 2 nm film). was set to experiment preferred N ₂ partial pressure obtained as a result (0.7 mTorr) shown in column a of table 2, 50.mu. a N ₂ partial pressure in the film forming atmosphere gas in the later this period
It shows the number of recording / erasing repetitions of an optical disk having a recording thin film formed by setting to Torr. This Table 2
From column B, when the N ₂ partial pressure in the film formation atmosphere gas at the start of the recording thin film formation process is increased and the thickness of the portion where the film is formed is too large (the N ₂ partial pressure is increased It can be seen that the repetition characteristics of recording / erasing of the optical disk are deteriorated when the thickness is larger than 3 nm.

Column C in Table 2 below shows various changes in the N ₂ gas partial pressure in the film formation atmosphere gas during the growth of the last film having a thickness of 2 nm before the end of the film formation process. The N ₂ partial pressure in the film forming atmosphere gas from the start to the above period is the preferable N ₂ obtained from the experimental results shown in Table 1 above.
_It shows the number of repetitions of recording / erasing of an optical disk having a recording thin film formed at a partial pressure of ₂ (50 μTorr). From column C of Table 2, it is found that N _{2 in} the film formation atmosphere gas during the period in which the film having the predetermined thickness is grown before the end of the film formation process.
When using a recording thin film formed by increasing the gas partial pressure from that in the film forming atmosphere gas during the period from the start of the process to the period, the recording / erasing of the optical disk is further repeated than the optical disk shown in Table 1. It can be seen that the characteristics are improved.

Column D in Table 2 below shows the partial pressure of N ₂ gas in the film formation atmosphere gas during the growth of the last film having a thickness of 2 to 5 nm before the end of the film formation process. C
The N ₂ partial pressure (0.7 mTorr) obtained from the experimental results shown in the column was set, and the N ₂ partial pressure in the film forming atmosphere gas from the start of the process to the period was 50 μTorr.
Indicates the number of repetitions of recording / erasing of an optical disk having a recording thin film formed by setting the recording thin film. From column D of Table 2, it is found that N in the film forming atmosphere gas before the film forming step of the recording thin film is completed.
_If the thickness of the film formed by increasing the partial pressure is too large (N
The thickness of the formed part to increase the _2-minute pressure is greater than 3nm If) can be seen that repetition characteristics of recording and erasing of an optical disk is decreased conversely.

[0041]

[Table 2]

From the above results of Tables 1 and 2, the improvement of the recording / erasing repetition characteristics is not only attributable to the improvement of the film quality of the recording thin film itself by the introduction of nitrogen into the recording thin film, but also to the process of forming the recording thin film. It was found that this was caused by the characteristics of the surface layer forming the interface with the protective layer formed by increasing the partial pressure of N ₂ gas in the film formation atmosphere gas at the start and end of the process.

Then, when the element composition ratio in the thickness direction of the recording thin film of the optical disk was examined by Auger electron spectroscopy (AES), an optical disk having particularly excellent recording / erasing repetition characteristics (recording / erasing repetition times of 21 Over 10,000 times), the surface layer including the surface serving as the interface with the protective layer of the recording thin film is in a nitrogen-rich state, and the nitrogen-rich surface layer is larger than the center in the thickness direction of the recording thin film. It had a nitrogen concentration at least three times higher.

From the above results, by setting the nitrogen concentration in the surface layer including the surface serving as the interface with the protective layer of the nitrogen-containing recording thin film to be higher than the nitrogen concentration in the central portion of the recording thin film, The repetition characteristics of recording and erasing can be significantly improved. (Especially, the repetition characteristics of recording and erasing of the optical disk can be significantly improved by setting the concentration at least three times higher than the nitrogen concentration at the center of the recording thin film.) Can be done). Also,
It has been found that the thickness of the surface layer portion where the nitrogen concentration is increased needs to be 3 nm or less, preferably 2-3 nm. In addition,
Although not described in Tables 1 and 2, the effect of improving the recording / erasing repetition characteristics was small when the thickness of the surface layer portion where the nitrogen concentration was increased was less than 1 nm.

Next, the effect of improving the recording / erasing repetition characteristics by increasing the nitrogen concentration in the surface layer portion of the recording thin film is related to the reference nitrogen concentration of the recording thin film (the nitrogen concentration in portions other than the surface layer portion). Average N ₂ in the film forming atmosphere gas during the film forming period of the portion other than the surface layer portion (2 nm thick portion from the start of film forming)
In each of the film forming process a partial pressure was variously changed, except N ₂ partial pressure / surface layer portion of the average in the average deposition period of N ₂ partial pressure (surface layer portion of the film forming atmosphere gas in the film formation period of the surface layer portion The recording thin film was formed by changing the average N ₂ partial pressure during the film formation period of the portion ( ₂ ), and the number of recording / erasing repetitions of the optical disk having each recording thin film was measured.

The results are shown in Table 3 below. From the measurement results, the average N ₂ partial pressure during the film formation period of the surface layer portion was calculated as 10% of the average N ₂ partial pressure during the film formation period of portions other than the surface layer portion. If it is twice or more, even if the average N ₂ partial pressure during the film formation period of the portion other than the surface layer portion is different, that is, even if the average nitrogen concentration of the portion other than the surface layer portion is different, remarkable recording / erasing is performed. It was found that the effect of improving the repetition characteristics of was obtained.

[0047]

[Table 3]

In the above experiment, the phase change material was Ge ₂ S
b ₂ was the experiment on recording thin film composed of Te _5, was subjected to Ge _x Sb _y Te _z same experiment as above by changing the composition ratio of compound, the composition ratio is 0.10 ≦
x ≦ 0.35, 0.10 ≦ y, 0.45 ≦ z ≦ 0.65, x
+ Y + z = 1, that is, A (35,1) in FIG.
0, 55), B (35, 20, 45), C (10, 4)
5,45), D (10,25,65), E (25,1)
(0, 65), when the composition has a composition in which both the crystallization sensitivity and the amorphization sensitivity are good (in consideration of overwriting by a single beam, the heating time required for crystallization is 1).
(When the time was set to 00 nsec or less), a remarkable effect of improving the recording / erasing repetition characteristics of the optical disk as described above was recognized.

The thickness of each layer on the optical disc is set to 0.
At least one of a period in which a film of a predetermined thickness grows after the start of film formation and a period in which a film of a predetermined thickness grows before the end of film formation in the process of forming a recording thin film, even if it is changed from larger than 100 nm to 100 nm. When the nitrogen concentration in the surface layer of the recording thin film is increased by increasing the nitrogen partial pressure in
It was recognized that the effect of improving the erase repetition characteristics was obtained. Similar results were obtained with an optical disc having no reflective layer.

In the process of forming a recording thin film, a different operation from the conventional one is performed only by controlling the partial pressure of nitrogen (N ₂ ) in the film forming atmosphere gas. It is expected that the ratio of the concentration change in the thickness direction (the ratio of the maximum concentration to the minimum concentration in the film thickness direction) will be smaller than the ratio of the concentration change of nitrogen in the film thickness direction. The correctness of this expectation was confirmed by AES analysis.

(Embodiment 2) In the first embodiment, the film formation atmosphere after a period in which a partial pressure of N ₂ in the film formation atmosphere gas is applied during the period in which the film of a predetermined thickness is grown at the start of the film formation step of the recording thin film. The N ₂ partial pressure in the film formation atmosphere gas during the period in which the film having the predetermined thickness is grown before the end of the film formation step is set to be larger than that in the gas or the film formation atmosphere from the start of the film formation step to the period By making it larger than that in the gas, the nitrogen concentration of the surface layer forming the interface with the protective layer in the recording thin film is made larger than that of the other parts, and the recording / recording of the optical disc is performed by the surface layer having this increased nitrogen concentration.
It has been described that the erase repetition characteristics are improved. In the second embodiment, the film forming speed in the period of growing the film having the predetermined thickness at the start of the process of forming the recording thin film is set to be smaller than the film forming speed after the predetermined period. The surface layer portion serving as the interface between the recording thin film and the protective layer by making the film formation rate during the period in which the film of the last predetermined thickness grows before the end of the step from the start of the film formation step until the period of the growth. Is made higher than that of the other portions, thereby improving the recording / erasing repetition characteristics of the optical disk.

First, the apparatus shown in FIG.
A phase-change optical disk was manufactured. The substrate is 1.
Phase change material that forms a recording thin film on a 2 mm glass substrate
Fee is Ge_TwoSb_TwoTe_Five And The protective layer is ZnS and SiO
_Two With a molar ratio (ZnS: SiO _Two ) 8: 2
And The reflection layer was made of Au. Membrane of each layer
The thickness is 100 nm in order from the protective layer on the substrate side (protective layer
2), 25 nm (recording thin film 3), 30 nm (protective layer)
4) 20 nm (reflection layer 5). Where the recording thin film
The pressure for forming a layer other than the above is 3 mTorr.
, And the film forming power was set to 100 W. one
On the other hand, when forming the recording thin film, the film formation atmosphere is Ar gas and N2.
_Two Gas mixture (partial pressure of Ar gas is 3mTorr
r, N_Two The gas partial pressure is 50 μTorr), and the deposition power is
Various changes. Various optical discs manufactured in this manner are
Repeated recording / erasing tests for each
Was. Here, the laser beam (wavelength: 780 nm) and the
The relative speed of the disc is 14m / sec and the shortest mark period
1.1μm random data 2-7 modulation mark position
Overwrites the recording of the
The change in ER was measured. First, the peak power and bias
BER change by independently changing the power in increments of 0.2 mW
And the BER value after repeating 100 times is 1 × 10
^-FiveLower the minimum power among the recording and erasing powers below.
Limited power. Repeated recording is 15% of the lower limit power
Repeated recording with additional recording / erasing power, BE
R is 1 × 10^-FiveThe number of repetitions when
It was measured. Table 4 shows the results.

[0053]

[Table 4]

Column A in Table 4 shows the number of repetitions of recording / erasing of an optical disk having a recording thin film formed with a constant film forming power from the start to the end of the film forming process. From column A of Table 4, when the entire recording thin film is formed with the same film forming power, if the film forming power is set to about 150 W and the recording thin film is formed, the optical disk provided with such a recording thin film has excellent recording performance. It can be seen that erasing repetition characteristics can be obtained.

Column B in Table 4 shows various changes in the film formation power during the growth of the film having a thickness of 2 nm after the start of the film formation in the film formation process of the recording thin film. Indicates the number of repetitions of recording / erasing of an optical disc having a recording thin film formed by setting a preferable film forming power (around 150 W) obtained from the experimental result shown in the column A of Table 4 above. I have. From column B in Table 4,
When the film forming power during the period in which the film having a thickness of 2 nm grows from the start of the film forming step of the recording thin film is lower than that in the other remaining periods, the recording / erasing repetition characteristics of the optical disk are improved, On the other hand, when it is increased, the recording / erasing characteristics of the optical disc tend to deteriorate, and particularly, the film forming power during the period of growth of the film having a thickness of 2 nm from the start of the film forming process and that during the other remaining periods. It can be seen that the recording / erasing repetition characteristics of the optical disk are drastically improved when it is reduced to 1/3 or less.

Column C in Table 4 shows various changes in the deposition power during the growth of the last 2 nm-thick film before the end of film formation in the recording thin film formation process, and the film formation from the start of the process to the said period. The power is shown in the column A of Table 4 and the number of repetitions of recording / erasing of the optical disc having the recording thin film formed by setting the preferable film forming power (about 150 W) obtained from the experimental results is shown. From column C of Table 4, when the film formation power during the period of growth of the last 2 nm thick film before the end of the film formation step of the recording thin film is reduced from that of the other remaining periods, the optical disk The repetition characteristics of recording and erasing of the optical disk are improved, and when raised, the repetition characteristics of recording and erasing of the optical disk tend to deteriorate. It can be seen that when the film forming power during the growing period is reduced to 1/3 or less of that during the remaining period, the recording / erasing repetition characteristics of the optical disk are dramatically improved.

The film forming power and the film forming speed of the recording thin film are proportional when the film forming power is in the range of 30 to 300 W. Therefore, in other words, from column B and column C in Table 4, the recording / erasing repetition characteristics of the optical disk when the film formation rate is reduced for a certain period from the start of the formation of the recording thin film or for a certain period before the end of the film formation. Especially when the film formation rate in a certain period from the start of film formation of the recording thin film or in a certain period before the end of film formation is reduced to 1/3 or less of the film formation rate in the other remaining periods. It can be seen that the repetition characteristics of recording and erasing are dramatically improved.

In general, when the film formation rate is low in a nitrogen atmosphere, the amount of nitrogen taken into the formed film increases,
Conversely, when the film formation rate is high, the amount of nitrogen taken into the formed film decreases. Therefore, from the above results, by controlling the film forming power in the film forming step of the recording thin film and increasing the nitrogen concentration in the surface layer portion including the surface serving as the interface with the protective layer of the recording thin film to be larger than that in the other portions. As in the case of Example 1, it was found that the recording / erasing repetition characteristics of the optical disk were improved. Then, when the element composition ratio in the thickness direction of the recording thin film of the optical disk was examined by AES, it was found that the optical disk having particularly excellent recording / erasing repetition characteristics (the number of recording / erasing repetitions is larger than 240,000 times) was not recorded. The surface layer portion including the surface forming the interface with the protective layer of the thin film is in a nitrogen-rich state, and the nitrogen-rich surface layer portion has a nitrogen concentration at least three times as large as the central portion in the thickness direction of the recording thin film. It was found to have.

Next, the period of increasing the film forming power from the start of the film forming step of the recording thin film or the period of increasing the film forming power before the end of the film forming step is changed to change the nitrogen concentration of the surface layer portion. When an experiment was performed to change the thickness, it was found that the thickness of the surface layer portion in which the nitrogen concentration was increased had to be 3 nm or less, preferably 2 to 3 nm, as in Example 1. In addition, when the thickness of the surface layer portion where the nitrogen concentration was increased was less than 1 nm, the effect of improving the recording / erasing repetition characteristics was small.

Next, the effect of improving the repetition characteristics of recording / erasing by increasing the nitrogen concentration in the surface layer portion of the recording thin film, which was confirmed by the above experiment, is based on the reference nitrogen concentration of the recording thin film (the nitrogen concentration in portions other than the surface layer portion). In order to confirm whether or not it can be generally obtained irrespective of the concentration, in each of the film forming steps in which the film forming power was changed variously during the film forming period of the portion other than the surface layer portion (2 nm thick portion from the start of film forming). The recording thin film is formed by changing the film forming power during the film forming period of the surface layer portion (the film forming power during the film forming period of the surface layer portion / the film forming power during the film forming period of portions other than the surface layer portion). An experiment was conducted to measure the number of recording / erasing repetitions of an optical disk having the above. As a result, if the average film forming power in the film forming period of the surface layer portion of the recording thin film is set to be not more than one third of the average film forming power in the film forming period of the portion other than the surface layer portion, the composition of the portion other than the surface layer portion is reduced. It was found that even when the average film forming power during the film period was different, that is, even when the nitrogen concentration contained in the portion other than the surface layer was different, a remarkable improvement in the repetition characteristics of recording / erasing was obtained. .

In the above experiment, the phase change material was Ge ₂ Sb ₂ Te
₅ was an experiment on a recording thin film consisting of Ge _x
Sb _y Te by changing the composition ratio of _z compound was subjected to the same experiment as above, the composition ratio is 0.10 ≦ x ≦ 0.
35, 0.10 ≦ y, 0.45 ≦ z ≦ 0.65, x + y + z
= 1, that is, a composition in which the crystallization sensitivity and the amorphization sensitivity within the range surrounded by A, B, C, D, and E in FIG. Considering writing, heating time required for crystallization is 100 nsec
At the time of the following), a remarkable effect of improving the recording / erasing repetition characteristics of the optical disk as described above was recognized.

The thickness of each layer on the optical disc is set to 0
Even when the thickness is changed from larger than 100 nm to 100 nm, the film formation power during the growth of a film having a predetermined thickness after the start of film formation in the film formation process of the recording thin film is reduced to increase the nitrogen concentration in the surface layer portion of the recording thin film. Thus, it was recognized that the effect of improving the recording / erasing repetition characteristics of the optical disk was obtained. Similar results were obtained with an optical disc having no reflective layer.

The rate of change of the nitrogen concentration in the film by controlling the film forming power (film forming speed) during the film forming process of the recording thin film depends on the exhaust capability of the film forming apparatus and various film forming conditions. A similar tendency was shown when the value was changed. Also, in the process of forming a recording thin film, an operation different from the conventional one is performed.
Since only the film formation power is controlled, the ratio of the concentration change of the element other than nitrogen in the film thickness direction (the ratio of the maximum concentration to the minimum concentration in the film thickness direction) is naturally larger than the concentration change ratio of nitrogen in the film thickness direction. It is expected to be smaller. The correctness of this expectation was confirmed by AES analysis.

Example 3 In Examples 1 and 2, the nitrogen concentration in the surface layer portion including the surface forming the interface with the protective layer of the recording thin film was made higher than that in the other portions, and this nitrogen concentration was increased. It has been described that the recording / erasing repetition characteristics of the optical disk are improved by the surface layer portion. In the third embodiment, the nitrogen concentration in the surface layer portion including the surface of the protective layer that forms the interface with the recording thin film is made higher than that in the other portions, and the recording / erasing of the optical disk is performed by the surface layer portion having the increased nitrogen concentration. This is to improve the repetition characteristics.

The method of increasing the nitrogen concentration in the surface layer portion of the protective layer of this embodiment is basically the same as that of the first embodiment, and controls the partial pressure of nitrogen (N ₂ ) in the atmosphere for forming the protective layer. Made by.

First, a phase-change optical disk having the layer configuration shown in FIG. 1 was manufactured using the apparatus shown in FIG. Here, the thickness and material of each layer are basically the same as those of the first embodiment,
The atmosphere for forming layers other than the protective layer is a pressure of 3 mT.
Only the orr Ar gas was used, and the film forming power was 100 W. On the other hand, the film forming power for forming the protective layer is 100 W
The film formation atmosphere was a mixed gas of Ar gas and N ₂ gas, the partial pressure of Ar gas was 3 mTorr, and the partial pressure of N ₂ gas was variously changed.

Repeated recording / erasing tests were performed on each of the various optical disks produced. Here, the relative speed between the laser beam (wavelength: 780 nm) and the disk is set to 14 m / sec, the random data is overwritten in the 2-7 modulation mark position with the shortest mark period of 1.1 μm, and the BER accompanying the number of repetitive recordings is increased. The change was measured. First, the BER change was measured by changing the peak power and the bias power independently at intervals of 0.2 mW, and
The minimum power among the recording / erasing powers at which the BER value after the repetition of 00 becomes 1 × 10 ⁻⁵ or less was defined as the lower limit power. Repeated recording is a recording with 15% increase of the lower limit power.
Repeated recording with erasing power, BER 1 × 10
^The number of repetitions when it became larger than ^-5 was measured.

In the first experiment, as shown in column A of Table 5 below, various optical discs having a protective layer formed by changing the partial pressure of N ₂ gas during the entire film forming process in various manners were used. They were fabricated and subjected to repeated recording / erasing tests. As a result, when forming the entire protective layer under a film formation atmosphere having the same nitrogen partial pressure, the N ₂ partial pressure is set to 5%.
It was found that when a film was formed in a film formation atmosphere of about 0 μTorr, an optical disk having such a recording thin film could obtain excellent recording / erasing repetition characteristics. An optical disc using such a protective layer formed at an appropriate partial pressure of N ₂ exhibits good cycle characteristics, for example, as described in Japanese Patent Application Laid-Open No.
No. 32133. However, a preferable N ₂ partial pressure strongly depends on film forming conditions (film forming apparatus to be used), and shows different values under different film forming conditions (film forming apparatus).

In the second experiment, as shown in the column B of Table 5, the partial pressure of the N ₂ gas in the film formation atmosphere gas was varied during the period of growth of the film having a thickness of 2 nm after the start of the film formation process. The recording / erasing repetition characteristics of the optical disk obtained by the experimental results shown in the column A of Table 5 above by changing the partial pressure of N ₂ gas in the film forming atmosphere gas after the period of growth of the film having a thickness of 2 nm. Various optical discs having a protective layer formed at a preferable partial pressure of N ₂ gas (50 μTorr) were prepared, and recording and erasing tests were repeatedly performed on these optical discs. As a result, the protective layer N ₂ gas content of film forming atmosphere gas after the period according to the N ₂ gas partial pressure in the film formation atmosphere gas in the period in which film is grown in the thickness of the process after the start 2nm in that the film forming step Pressure (50μTorr)
It was found that the larger the size, the more the recording / erasing repetition characteristics of the optical disk were further improved.

In the third experiment, as shown in the column C of Table 5 below, the N ₂ gas partial pressure in the film formation atmosphere gas during the period of growth of the film having a thickness of 2 to 20 nm after the start of the film formation process. Is set to 0.7 mTorr, which makes the recording / erasing repetition characteristics of the optical disk obtained from the experimental results shown in the column B of Table 5 the most excellent, and the composition after the period of growth of the 2-20 nm thick film is obtained. The N ₂ gas partial pressure in the film atmosphere gas is set to a preferable N ₂ gas partial pressure (50 μTorr) for improving the recording / erasing repetition characteristics of the optical disk obtained by the experimental results shown in column A of Table 5 above. Various optical disks having a protective layer formed by the above method were manufactured, and a recording / erasing repeated test was performed on these optical disks. As a result, if the surface layer portion formed by increasing the N ₂ partial pressure in the film forming atmosphere gas of the protective layer is too large (when the thickness of the surface layer portion formed by increasing the N ₂ partial pressure becomes larger than 10 nm), the optical disk is formed. Records of
It was found that the repetition characteristics of the erasure deteriorated.

In the fourth experiment, as shown in the column D of Table 5, the N ₂ gas content in the film formation atmosphere gas during the growth of the last film having a thickness of 2 nm at the end of the film formation process is shown. The pressure was changed variously, and the partial pressure of N ₂ gas in the film forming atmosphere gas from the start of the process to the above period was excellent in the recording / erasing repetition characteristics of the optical disk obtained by the experimental results shown in column A of Table 5 above. N ₂ gas partial pressure (50
Various optical discs having a protective layer formed at (μTorr) were produced, and repeated recording / erasing tests were performed on these optical discs. As a result, the protective layer is formed in the film formation atmosphere gas before the period in which the partial pressure of N ₂ gas in the film formation atmosphere gas is applied during the period in which the last film having a thickness of 2 nm is grown at the end of the film formation in the film formation process. N ₂ gas partial pressure (50 μTorr)
It has been found that, when formed to be larger than r), the recording / erasing repetition characteristics of the optical disk are further improved.

In the fifth experiment, as shown in column E of Table 5 below, the last 2 to 20
N in the film forming atmosphere gas during the period when the film having a thickness of nm is grown.
_{(2) The} gas partial pressure is set to 0.7 mTorr so as to maximize the recording / erasing repetition characteristics of the optical disk obtained from the experimental results shown in the column D of Table 5 above, and the ₂ to 20 nm thick film from the start of the process. preferred N ₂ but to have a high repetition characteristics of recording and erasing of an optical disk obtained the N ₂ gas partial pressure of the film forming atmosphere gas up period to grow by experimental results shown in column a of table 5 Gas partial pressure (50μ
Various optical discs having a protective layer formed according to (Torr) were manufactured, and repeated recording / erasing tests were performed on these optical discs. As a result, if the surface layer portion formed by increasing the N ₂ partial pressure in the film formation atmosphere gas in the protective layer is too large (N ₂
(When the thickness of the surface layer formed by increasing the partial pressure is larger than 10 nm), the repetition characteristics of recording / erasing of the optical disk are found to be reduced.

[0073]

[Table 5]

From the results shown in Table 5, the improvement in the recording / erasing repetition characteristics is not only attributable to the improvement of the film quality of the recording thin film itself due to the introduction of nitrogen into the recording thin film, but also at the start of the step of forming the protective layer. It was found that the characteristics were attributable to the characteristics of the surface layer portion including the surface serving as an interface with the recording thin film formed by increasing the partial pressure of N ₂ gas in the film forming atmosphere gas at the end of the process.

Then, when the element composition ratio in the thickness direction of the protective layer of the optical disk was examined by AES, it was found that the optical disk having particularly excellent recording / erasing repetition characteristics (the number of recording / erasing repetitions was 200,000 or more) was obtained. The surface layer of the protective layer including the surface forming the interface with the recording thin film is in a nitrogen-rich state, and the nitrogen-rich surface layer has at least three times more nitrogen than the central part in the thickness direction of the protective layer. It was found to have a concentration.

From the above results, by setting the nitrogen concentration of the surface layer including the surface serving as the interface with the recording thin film of the nitrogen-containing protective layer to be higher than the nitrogen concentration of the central part of the protective layer, the optical disk is improved. The repetition characteristics of recording / erasing can be greatly improved (especially, by setting the concentration at least three times higher than the nitrogen concentration at the center of the protective layer,
It is found that the repetition characteristics of recording / erasing of the optical disk can be surely significantly improved). Further, it was found that the thickness of the surface layer portion in which the nitrogen concentration was increased needs to be 10 nm or less, preferably 1 to 10 nm. In addition,
Although not described in Table 5, when the thickness of the surface layer portion where the nitrogen concentration was increased was less than 1 nm, the effect of improving the recording / erasing repetition characteristics was small.

Next, the effect of improving the recording / erasing repetition characteristics by increasing the nitrogen concentration in the surface portion of the protective layer is as follows.
In order to check whether or not the protective layer can be generally obtained irrespective of the reference nitrogen concentration of the protective layer (the nitrogen concentration of the portion other than the surface portion), the film is formed in a portion other than the surface portion (2 nm thick portion from the start of the film formation). in each of the film forming process having various average of N ₂ partial pressure in the film formation atmosphere gas during the period, the formation of the average of the N ₂ partial pressure (surface layer portion of the film formation atmosphere gas in the film formation period of the surface layer portion change the average N ₂ partial pressure) in the deposition period of N ₂ partial pressure / surface layer portion other than the portion of the average of the period to form a protective layer, the number of repetitions of recording and erasing of an optical disc having the protective layer It was measured. As a result, if the average N ₂ partial pressure in the film forming period of the surface layer portion of the protective layer is made larger than the average N ₂ partial pressure in the film forming period of the portion other than the surface layer portion, the film forming period of the portion other than the surface layer portion is reduced. It was found that, even when the average N ₂ partial pressure was different, that is, even when the average nitrogen concentration in the parts other than the surface layer was different, a remarkable effect of improving the recording / erasing repetition characteristics was obtained.

The thickness of each layer on the optical disk is set to 0.
At least one of a period in which a film having a predetermined thickness is grown after the start of film formation and a period in which a film having a predetermined thickness is grown before the end of film formation in the step of forming a protective layer, even when the film thickness is changed from larger than 100 nm to 100 nm. It was confirmed that increasing the nitrogen partial pressure in Example 1 to increase the nitrogen concentration in the surface layer portion of the protective layer could improve the recording / erasing repetition characteristics of the optical disk. Similar results were obtained with an optical disc having no reflective layer.

The above results indicate that the dielectric material is Zn
This is an experimental result of an optical disc provided with a protective layer containing S and SiO _2, and it is shown that a protective layer containing ZnS alone as a dielectric material, a protective layer containing SiO ₂ alone, ZnS and SiO ₂ Similar results could be obtained for an optical disk having at least one selected layer and a protective layer containing Ta ₂ O ₅ .

In the process of forming the protective layer, the operation different from the conventional one is performed only by controlling the partial pressure of nitrogen (N ₂ ) in the film forming atmosphere gas. It is expected that the ratio of the concentration change in the thickness direction (the ratio of the maximum concentration to the minimum concentration in the film thickness direction) will be smaller than the ratio of the concentration change of nitrogen in the film thickness direction. The correctness of this expectation was confirmed by AES analysis.

(Embodiment 4) In Embodiment 3, the N ₂ partial pressure in the film formation atmosphere gas during the period in which the film of a predetermined thickness is grown at the start of the process of forming the protective layer is performed. The N ₂ partial pressure in the film formation atmosphere gas during the period in which the film having the predetermined thickness is grown before the end of the film formation step is set to be larger than that in the gas or the film formation atmosphere from the start of the film formation step to the period By making it larger than that in the gas, the nitrogen concentration in the surface layer which forms the interface with the recording thin film in the protective layer is made higher than that in other parts, and recording / erasing of the optical disk is performed by the surface layer with this increased nitrogen concentration. It has been described that the repetition characteristic of is improved. In the fourth embodiment, the film formation rate in the period in which the film having the predetermined thickness is grown at the start of the film formation in the protection layer formation step is set to be smaller than the film formation rate after the period, or The surface layer portion forming the interface with the recording thin film of the protective layer is formed by setting the film forming rate in the period during which the last film having the predetermined thickness grows before the step is completed to be smaller than the film forming rate from the start of the film forming step to the period. The nitrogen concentration is made higher than that of the other portions, thereby improving the recording / erasing repetition characteristics of the optical disk.

First, a phase-change optical disk having the layer configuration shown in FIG. 1 was manufactured using the apparatus shown in FIG. Here, the thickness and material of each layer were basically the same as those of the first embodiment. Here, the film formation atmosphere for forming layers other than the protective layer was only Ar gas at a pressure of 3 mTorr, and the film formation power was 100 W. On the other hand, the film formation atmosphere for forming the protective layer was a mixed gas of Ar gas and N ₂ gas (the partial pressure of the Ar gas was 3 mTorr and the partial pressure of the N ₂ gas was 50 μTorr), and the film forming power was variously changed. . Repeated recording / erasing tests were performed on each of the various optical disks thus manufactured. Here, the laser beam (wavelength: 7)
80 nm) and the relative speed of the disk is 14 m / sec, and the shortest mark period is 1.1 μm and random data is 2-
The 7 modulation mark position recording was overwritten, and the change in BER with the number of repeated recordings was measured. First, the BER change is measured by independently changing the peak power and the bias power at intervals of 0.2 mW, and the minimum power among the recording / erasing powers at which the BER value after repeating 100 times becomes 1 × 10 ⁻⁵ or less is determined. The lower limit power was used. Repeat records
Repetitive recording was performed with a recording / erasing power 15% higher than the lower limit power, and the number of repetitions when the BER became larger than 1 × 10 ⁻⁵ was measured. Table 6 shows the results.

[0083]

[Table 6]

Column A in Table 6 shows the number of repetitions of recording / erasing of an optical disk having a protective layer formed with a constant film forming power from the start to the end of the film forming step. From column A in Table 6, when the entire protective layer is formed with the same film forming power, when the film forming power is set to 100 to 150 W, the optical disk provided with such a protective layer has excellent recording / erasing performance. It can be seen that repetition characteristics can be obtained.

Column B in Table 6 shows various changes in the film formation power during the growth of the film having a thickness of 2 nm after the start of film formation in the process of forming the protective layer. Indicates the number of repetitions of recording / erasing of the optical disk having the protective layer formed by setting the preferable film forming power (100 W) obtained from the experimental result shown in the column A of Table 6 above. . From column B of Table 6, when the film formation power during the period of growth of the film having a thickness of 2 nm from the start of the process of forming the protective layer is lower than that during the other remaining periods, the recording / recording of the optical disk is performed. Erasure repeatability is improved,
On the other hand, it can be seen that when it is raised, the recording / erasing characteristics of the optical disc tend to deteriorate.

Column C in Table 6 shows various changes in the deposition power during the growth of the last 2 nm-thick film before the completion of the deposition in the deposition process of the protective layer, and the deposition from the start of the process to the above-mentioned period. The figure shows the number of recording / erasing repetitions of an optical disc having a protective layer formed by setting the power to a preferable film forming power (about 100 W) obtained from the experimental results shown in the column A of Table 6 above. From column C in Table 6, when the film formation power during the period of growth of the last 2 nm-thick film before the end of the protection layer film formation step is reduced from that of the other remaining periods, the optical disk It can be seen that the recording / erasing repetition characteristics of the optical disc are improved, and conversely, when the recording / erasing repetition characteristics are increased, the recording / erasing repetition characteristics of the optical disk tend to deteriorate.

The film forming power and the film forming speed of the protective layer are proportional when the film forming power is in the range of 30 to 300 W. Therefore, in other words, from the columns B and C in Table 6, the film formation rate in a certain period from the start of the formation of the protective layer or in a certain period before the end of the film formation is smaller than the film formation rate in the other remaining periods. It can be seen that the repetition characteristics of recording / erasing of the optical disk are improved in the case of performing the above.

In general, when the film formation rate is low in a nitrogen atmosphere, the amount of nitrogen taken into the formed film increases.
Conversely, when the film formation rate is high, the amount of nitrogen taken into the formed film decreases. Therefore, from the above results, by controlling the film forming power in the protective layer film forming step to increase the nitrogen concentration in the surface layer portion including the surface of the protective layer which is the interface with the recording thin film, to be higher than that in the other portions. As in the case of the third embodiment, it was found that the recording / erasing repetition characteristics of the optical disk were improved. Then, when the elemental composition ratio of the protective layer of the optical disk in the film thickness direction was examined by AES, the optical disk having particularly excellent recording / erasing repetition characteristics has a surface layer portion including the surface of the protective layer which is the interface with the recording thin film. It is in a nitrogen-rich state, and it has been found that such a nitrogen-rich surface layer portion has a nitrogen concentration at least three times or more as compared with the central portion in the thickness direction of the recording thin film.

Next, the period for increasing the film forming power from the start of the step of forming the protective layer or the period for increasing the film forming power before the end of the step of forming the film is changed so that the nitrogen concentration in the surface layer portion is increased. When an experiment was performed to change the thickness, it was found that the thickness of the surface layer portion in which the nitrogen concentration was increased had to be 10 nm or less, preferably 1 to 10 nm, as in Example 3. In addition, the thickness of the surface layer portion where the nitrogen concentration is increased is 1 nm.
When the value is less than the above, the effect of improving the repetition characteristics of recording / erasing was small.

Next, the effect of improving the recording / erasing repetition characteristics by increasing the nitrogen concentration in the surface layer portion of the protective layer, which was confirmed by the above experiment, is based on the reference nitrogen concentration of the protective layer (the nitrogen concentration in portions other than the surface layer portion). In order to confirm whether or not it can be generally obtained irrespective of the concentration, in each of the film forming steps in which the film forming power was changed variously during the film forming period of the portion other than the surface layer portion (2 nm thick portion from the start of film forming). The protective layer is formed by changing the film forming power during the film forming period of the surface layer portion (the film forming power during the film forming period of the surface layer portion / the film forming power during the film forming period of portions other than the surface layer portion). An experiment was conducted to measure the number of recording / erasing repetitions of an optical disk having the above. As a result, when the average film forming power in the film forming period of the surface layer portion of the protective layer is smaller than the average film forming power in the film forming period of the portion other than the surface layer portion, the average film forming power of the portion other than the surface layer portion during the film forming period is reduced. It was found that even if the film forming power was different, that is, even if the nitrogen concentration contained in portions other than the surface layer portion was different, remarkable improvement in the repetition characteristics of recording / erasing could be obtained.

The thickness of each layer on the optical disk is set to 0.
Even when the thickness is changed from larger than 100 nm to 100 nm, the film formation power during the growth of a film having a predetermined thickness after the start of film formation in the film formation process of the protective layer is reduced to increase the nitrogen concentration in the surface layer portion of the protective layer. Thus, it was recognized that the effect of improving the recording / erasing repetition characteristics of the optical disk was obtained. Similar results were obtained with an optical disc having no reflective layer.

The above results indicate that the dielectric material is Zn
This is an experimental result of an optical disc provided with a protective layer containing S and SiO _2, and it is shown that a protective layer containing ZnS alone as a dielectric material, a protective layer containing SiO ₂ alone, ZnS and SiO ₂ Similar results could be obtained for an optical disk having at least one selected layer and a protective layer containing Ta ₂ O ₅ .

The rate of change of the nitrogen concentration in the film by controlling the film forming power (film forming rate) during the process of forming the protective layer depends on the exhaust capability of the film forming apparatus and various film forming conditions. A similar tendency was shown when the value was changed. In addition, it is conceivable that the concentration of elements other than nitrogen in the protective layer changes in the film thickness direction by controlling the film forming power (film forming speed) during the film forming process of the protective layer. As a result, the rate of change in the concentration of elements other than nitrogen was extremely small as compared with that of the nitrogen concentration.

[0094]

As described above, according to the present invention, at least one of the recording thin film and the protective layer in the phase-change optical information recording medium contains nitrogen. At least one of the constituent elements, the element having the largest rate of change in concentration in the thickness direction of the thin film (layer) among the constituent elements, is nitrogen, and the surface layer portion including the surface serving as an interface between the recording thin film and the protective layer. By setting the nitrogen concentration to be higher than the nitrogen concentration in the portion other than the surface layer portion, it is possible to obtain a phase-change optical information recording medium in which the recording / erasing repetition characteristics are dramatically improved.

Further, according to the present invention, a phase change type optical information recording medium capable of rational and stable manufacture of a phase change type optical information recording medium having a remarkably improved recording / erasing repetition characteristic can be manufactured. Can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a specific example of a phase change type optical information recording medium of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of another specific example of the phase-change optical information recording medium of the present invention.

FIG. 3 is a view schematically showing a magnetron sputtering apparatus used for forming each layer at the time of manufacturing a phase change optical disc according to an embodiment of the present invention.

FIG. 4 is a diagram schematically showing an evaluation apparatus used for a repetitive recording / erasing test of a phase change optical disk according to an embodiment of the present invention.

FIG. 5 is a diagram showing intensity modulation of laser power when recording is repeatedly performed on a phase change optical disc according to an embodiment of the present invention.

6 is a diagram showing the composition range of Ge _x Sb _y Te _Z of the recording thin film of the phase change optical disk according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1a Substrate surface 2 Protective layer 2a Surface part 3 Recording thin film 3a, 3b Surface part 4 Protective layer 4a Surface part 5 Reflective layer 6 Adhesive layer 7 Protective substrate 8 Laser beam

Claims (24)

[Claims] 1. A base material, a recording thin film disposed on the base material, containing nitrogen as a constituent element, and having a reversibly changing optical characteristic before and after irradiation with a laser beam. In a phase-change optical information recording medium having a protective layer formed on one surface or both surfaces, the recording thin film has the largest percentage of the change in concentration of the constituent elements in the thickness direction of the thin film. The element is nitrogen, and a surface layer portion including a surface forming an interface with the protective layer has a high nitrogen concentration necessary to substantially suppress interdiffusion between the recording thin film and the protective layer. A phase change type optical information recording medium characterized by the above-mentioned. 2. An average nitrogen concentration in a portion having a thickness of 2 nm from a surface forming an interface with a protective layer of a recording thin film is equal to the average nitrogen concentration.
2. The phase-change type optical information recording medium according to claim 1, wherein the average nitrogen concentration of the portion other than the portion having a thickness of nm is three times or more. 3. The phase change optical information recording medium according to claim 1, wherein the phase change material constituting the recording thin film is a chalcogen compound containing at least one selected from Se and Te. 4. A chalcogen compound Ge _x Sb _y Te _z
(0.10 ≦ x ≦ 0.35, 0.10 ≦ y, 0.45 ≦
5. The phase-change optical information recording medium according to claim 4, wherein z ≦ 0.65, x + y + z = 1). 5. The protective layer is made of ZnS, SiO ₂ and Ta ₂ O.
At least one dielectric phase change type optical information recording medium according to claim 1 substances are those which comprise selected from _5. 6. A base material, a recording thin film having optical properties reversibly changed before and after irradiation of a laser beam disposed on the base material, and formed on one surface or both surfaces of the recording thin film. And a protective layer containing nitrogen as a constituent element thereof, wherein the protective layer has the highest rate of change in concentration of the constituent elements in the thickness direction of the layer. The bigger element is nitrogen,
And a surface layer portion including a surface forming an interface with the recording thin film has a high nitrogen concentration necessary to substantially suppress interdiffusion between the recording thin film and the protective layer. A changeable optical information recording medium. 7. An average nitrogen concentration in a portion having a thickness of 2 nm from a surface forming an interface with the recording thin film of the protective layer is equal to the average nitrogen concentration.
7. The phase-change optical information recording medium according to claim 6, wherein the average nitrogen concentration of the portion other than the portion having a thickness of nm is three times or more. 8. The protective layer is made of ZnS, SiO ₂ and Ta ₂ O.
At least one dielectric phase change type optical information recording medium according to claim 6 or 7 substances are those which comprise selected from _5. 9. A protective layer comprising ZnS and SiO ₂ in a molar ratio (Z
nS: SiO 2) 8: phase-change optical information recording medium according to the which claim 8 which comprises a mixing ratio of _2. 10. A phase change material constituting a recording thin film is Se.
10. The phase-change optical information recording medium according to claim 6, which is a chalcogen compound containing at least one selected from the group consisting of and Te. 11. The method for manufacturing a phase-change optical information recording medium according to claim 1, wherein the film is formed in a film forming atmosphere gas during a period of forming a surface layer portion including a surface forming an interface with the protective layer. nitrogen gas (N ₂₎ concentration, forming a film of average nitrogen gas (N ₂₎ recording thin film was greater than the concentration of the film forming atmosphere gas in the period for forming the portion other than the surface layer portion A method for producing a phase-change optical information recording medium, characterized by comprising: 12. An average nitrogen gas (N ₂ ) concentration in a film forming atmosphere gas during a period in which a portion having a thickness of 2 nm is formed from a surface forming an interface with a protective layer of a recording thin film, 10% of the average nitrogen gas (N ₂ ) concentration in the film forming atmosphere gas during the period of forming the portion other than the portion having the thickness.
The method for manufacturing a phase-change optical information recording medium according to claim 11, wherein the recording thin film is formed by multiplying the thickness by at least twice. 13. The method for manufacturing a phase-change optical information recording medium according to claim 1, wherein an average film forming rate during a period of forming a surface portion including a surface forming an interface with the protective layer is formed. Wherein the recording thin film is formed at a speed smaller than an average film forming rate during a period of forming a portion other than the surface layer portion. 14. An average film forming rate during a period in which a portion having a thickness of 2 nm is formed from a surface forming an interface with a protective layer of a recording thin film, and a portion other than the portion having the thickness of 2 nm is formed. 14. The method of manufacturing a phase-change optical information recording medium according to claim 13, wherein the recording thin film is formed at a rate equal to or less than one third of the average film forming rate during the period. 15. A phase change material constituting a recording thin film is Se.
The method for producing a phase-change optical information recording medium according to any one of claims 11 to 14, which is a chalcogen compound containing at least one selected from the group consisting of Te and Te. 16. chalcogen compound Ge _x Sb _y Te _z
(0.10 ≦ x ≦ 0.35, 0.10 ≦ y, 0.45 ≦
The method according to claim 15, wherein z ≦ 0.65, x + y + z = 1). 17. The protective layer is made of ZnS, SiO ₂ and Ta _2.
At least one method of manufacturing the phase-change optical information recording medium according to any one of claims 11 to 16 dielectric materials are those which comprise selected from O _5. 18. The method for manufacturing a phase-change optical information recording medium according to claim 6, wherein the film is formed in a film forming atmosphere gas during a period of forming a surface layer portion including a surface forming an interface with the recording thin film. average nitrogen gas (N ₂₎ concentration of, forming the protective layer be larger than the nitrogen gas (N ₂₎ concentration of the average film forming atmosphere gas in the period for forming the portion other than the surface layer portion A method for producing a phase change type optical information recording medium, characterized by comprising: 19. An average nitrogen gas (N ₂ ) concentration in a film forming atmosphere gas during a period of forming a portion having a thickness of 2 nm from a surface forming an interface with a recording thin film of a protective layer, 10% of the average nitrogen gas (N ₂ ) concentration in the film forming atmosphere gas during the period of forming the portion other than the portion having the thickness.
19. The method for manufacturing a phase-change optical information recording medium according to claim 18, wherein the protective layer is formed at twice or more times. 20. The method for manufacturing a phase-change optical information recording medium according to claim 6, wherein an average film forming rate during a period of forming a surface layer portion including a surface forming an interface with the recording thin film. A phase-change optical information recording medium, wherein the protective layer is formed at a rate smaller than an average film forming rate during a period in which a portion other than the surface layer is formed. 21. An average film forming rate during a period in which a portion having a thickness of 2 nm is formed from a surface forming an interface with a recording thin film of a protective layer, and a portion other than the portion having the thickness of 2 nm is formed. 21. The method for manufacturing a phase-change optical information recording medium according to claim 20, wherein the protective layer is formed at a rate equal to or less than one-third of the average film forming rate during the period. 22. The protective layer is made of ZnS, SiO ₂ and Ta _2.
At least one method of manufacturing the phase-change optical information recording medium according to any one of claims 18 to 21 dielectric materials are those which comprise selected from O _5. 23. The method according to claim 22, wherein the protective layer comprises ZnS and SiO ₂ in a molar ratio (ZnS: SiO ₂ ) of 8: 2. . 24. The phase change material constituting the recording thin film is Se
24. The method for producing a phase-change optical information recording medium according to claim 19, wherein the method is a chalcogen compound containing at least one selected from the group consisting of Te and Te.