JPH045080A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the oxidation of a recording film and to enhance recording and reproducing characteristics by providing a part where the content of a passive state forming metal is higher than the average content thereof in the recording film in the vicinity of the interface of the recording film with a substrate or the surface thereof or to both of them. CONSTITUTION:An optical recording medium consists of a substrate and a recording film containing at least one kind of an element selected from Sn, Bi and Sb, Se and a passive state forming metal element. A part where the content of a passive state forming metal element is higher than the average content thereof in the recording film is provided in the vicinity of the interface of the recording film with the substrate or the surface thereof or to both of them. The part high in the content of the passive state forming metal element is oxidized by oxygen or moisture in air and, since a thin stable layer composed of oxide is formed to prevent the advance of the oxidation of the recording film, the recording medium having high oxidation resistance is obtained. Further, the shape of a pit at the time of recording is enhanced and the optical recording medium wherein the CN ratio of a reproducing signal is enhanced and the CN ratio of a reproducing signal is enhanced and the error of reproducing data is reduced is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention enables recording by condensing and irradiating a laser beam onto a thin recording film formed on a substrate and heating and melting the irradiated portion. The present invention relates to an optical recording medium in which high-density information is recorded by forming pits in a film and can be reproduced by utilizing changes in the light reflectance of the recorded portion.

[Prior art]

2. Description of the Related Art Conventionally, a method has been known in which a laser beam is focused and irradiated onto a recording film formed on a transparent substrate such as glass or plastic, thereby recording and reproducing information on the recording film. One of these recording and reproducing methods is to record information by irradiating the recording film with a laser beam, locally heating and melting the recording film, and forming small holes called pits. A known method is to irradiate a recording film surface with a laser beam and detect the reflected light to reproduce information. The recording film used in this method has conventionally been made of low-melting point metals such as Te, Sb, and Sn, or alloys containing these as main components, or composites with organic substances or oxides by methods such as vapor deposition or sputtering. Thin films, and even thin films formed by spin coating or other methods using organic dyes having a light absorption band in the near-infrared region, are known.

In particular, recording films made of low melting point metals and alloys containing these as main components are widely used because they provide relatively good recording and reproducing characteristics.

[Problem to be solved by the invention]

These low melting point metal thin films have the disadvantage of being easily oxidized by oxygen or moisture when left in the atmosphere. When the recording film is oxidized, the light transmittance increases and the light absorption rate decreases, which reduces the energy absorption of laser light, and also increases the melting point, which increases the energy required to form pits. The recording sensitivity of the recording medium decreases.

At the same time, there are also problems such as a decrease in the CN ratio and an increase in the error rate due to the deterioration of the pit shape, and an increase in the error rate due to the occurrence of pitting corrosion.

In order to solve these problems, it is widely practiced to prevent the oxidation of the recording film by adding elements such as C5Se to the above-mentioned low melting point metal film, but this method also reduces the lifetime. remains insufficient. Furthermore, the CN ratio during recording and reproduction is still insufficient, and a disk with excellent recording and reproduction characteristics is desired.

[Means to solve the problem]

In order to solve such problems, the present invention provides a recording film provided on a substrate containing at least one element selected from the group consisting of Sn and BISSb, Se, and a passive state forming metal element, and It is characterized by having a portion near the interface between the film and the substrate, near the surface on the opposite side thereof, or both, where the content of the passive state forming metal is higher than the average content of the passive state forming metal element of the recording film.

That is, the content of the passive state-forming metal provided near the surface or near the interface with the substrate, or both, of alloy thin films such as 5nSe, B1Se, and 5bSe, which provide recording films with high sensitivity and relatively high oxidation resistance, is The large portion is oxidized by oxygen and moisture in the air, forming an extremely thin and stable layer of oxide, which prevents oxygen from reaching the inside of the recording film and prevents the progress of oxidation of the recording film. This method provides a recording medium with extremely high oxidation resistance.

Furthermore, by providing a portion with a high content of passive state-forming metal as described above, the shape of the pit during recording is improved, resulting in an improved CN ratio of the reproduced signal, lower jitter, and fewer errors in the reproduced data. A highly reliable optical recording medium can be obtained.

An example of the layer structure of the recording film in the present invention is shown in FIG.

In the recording film of the present invention, if the content of the passive state-forming metal is high, the recording sensitivity decreases significantly, and if the content is low, sufficient oxidation resistance cannot be obtained. A preferable range is 5% or more and 20% or less in terms of atomic percent. Furthermore, in order to protect the inside of the recording film from oxidation, it is necessary to form a stable oxide layer of sufficient thickness on the substrate side of the recording film or on the surface opposite to the substrate. The portion containing the metal that forms the action state has a thickness of 0.5 mm on both the substrate side and the surface opposite to the substrate. Although it is preferable that the thickness is 5 nm or more, the other portions may not contain all of the passive state forming metal.

In the present invention, the above-mentioned effects can be observed whether the portion containing a large amount of passive state-forming metal is provided on the substrate side of the recording film or on the surface opposite to the substrate.
It is particularly preferable to provide the film on both surfaces opposite to the substrate because the oxidation resistance of the recording film is significantly improved.

Examples of the passive state forming metal elements in the present invention include AI
, Ti, Cr, Go, Ni5Nb, Ta, etc. Any of these may be used, but TI or Cr
is particularly preferable because it forms a stable passive layer even if it is an extremely thin film.

The film thickness of the recording film in the present invention is determined by reflectance, recording sensitivity, CN
From the viewpoint of recording characteristics such as ratio, a range of 5 nm or more and 60 rv or less is preferable. Furthermore, the composition ratio of Se in the recording film excluding the passive state-forming metal element in the recording film in the present invention is, for example,
20-60% when the recording film is composed of Se and Sn;
When consisting of Se and Bi or Se and sb, 30~
A range of 80% is preferable, and within this range, a recording film with good recording properties such as a high CN ratio and high recording sensitivity can be obtained. Further, other elements having a low melting point may be added to the recording film in a composition ratio of 10% or less for the purpose of controlling optical properties such as light absorption and light reflectance. Examples of the low melting point element to be added include GesTe, In, and the like.

In the present invention, the recording film of the recording medium is generally formed using a physical thin film forming method such as a vacuum evaporation method or a sputtering method, and each layer is formed while maintaining a vacuum in the vacuum chamber of these devices. It is preferable to form the film continuously. Further, in order to form an oxide layer on the surface of the recording film and to perform stable recording and reproduction over time, an oxidation treatment such as heating in air may be performed after forming the recording film of the present invention.

The substrate used in the present invention is a glass substrate, a thermoplastic resin substrate such as polymethyl methacrylate, polycarbonate, or polyolefin, a thermosetting resin substrate such as epoxy resin, or a recording film of the above substrate is formed for the purpose of providing groups, etc. Any transparent substrate used for general optical recording media may be used, such as a substrate coated with ultraviolet curable resin or the like on the recording side. The recording film of the present invention may be formed after forming or coating an organic or inorganic underlayer on the substrate.

〔Example〕

The present invention will be explained in detail below using examples.

Example 1 Thickness 1. 2mm, outer diameter 130mm disk with 1.
A substrate made of polycarbonate resin having spiral groups with a pitch of 6 μm was fabricated.

It was placed in the sputtering chamber of the sputtering equipment.

In addition, a SnSn5aSe target was added to the RF cathode.
A Ti target was attached to the C cathode. After the sputtering chamber was evacuated to I x 10-' torr, argon gas was introduced and the pressure was adjusted so that the degree of vacuum was 5 x 10-' torr.
Two-dimensional simultaneous sputtering was performed on the nSn5sSe target until the film thickness was 2.5 mm. A 5 nm Ti5n-Se alloy film was produced. At this time, the composition of the alloy film is Tea. (5nssSe□
)6. The power input to both targets was adjusted so that

Next, sputtering was performed only on the Sn4@Segm target to form a film with a thickness of 1 on the previously formed Ti-Sn-Se alloy film.
A 2.5nu 5nasSe,s film was laminated. Furthermore, Tj -Sn -S with a film thickness of 2.5 nm was formed using the same method as above.
e alloy films were laminated.

The recording and reproducing characteristics of the recording film formed by the above method were measured. The measurement was carried out using a semiconductor laser with a wavelength of 830 nm, a disk rotation speed of 180 Orpm, and a recording frequency of 3. Recording and reproduction were performed under the condition of 7 MHz, and the CN ratio of the reproduced signal was measured using a spectrum analyzer.

The results are shown in FIG. Next, hold the above recording medium at 75°.
An accelerated environmental resistance test was conducted by leaving the sample in a constant temperature and humidity chamber at 85% RH. FIG. 3 shows the change in byte error rate up to 2000 hours of neglect. Here, the byte error rate is calculated by performing (2-7) RLL modulation on random data, recording it on a disk rotating at 180° rpm, and comparing the reproduced data with the recorded data. number divided by the total number of recorded bytes.

The results show that the recording film of this example exhibits good recording and reproducing characteristics, and the deterioration of the recording and reproducing characteristics is extremely small even under severe conditions.

Comparative Example 1 On a polycarbonate substrate similar to that used in Example 1, only one Sn5m5esi film was deposited in the same manner as in Example 1.
The film was formed to a film thickness of 7.5r+m.

The recording and reproducing characteristics of the recording film formed by the above method were measured in the same manner as in Example 1, and the results are shown in FIG. Furthermore, the results of the accelerated environmental resistance test are shown in Figure 3.

From the results shown in FIG. 2.3, it can be seen that the recording film of this comparative example is inferior to the recording film of Example 1 in both recording and reproducing characteristics and environmental resistance.

Example 2 A Ti-5n-Se alloy film and a 5n
-Se alloy film and Ti-Sn-Se alloy film were sequentially laminated. At this time, Ti-Sn on both sides of the 5n-Se alloy film
-The film thickness of the Se alloy film was kept constant at 3 nm, and the Ti
and Sn@@Ses* by changing the power applied to the target and changing the composition Tin (SnsiSesi) r. . The value of X at -8 was changed.

A recording/reproducing test and an accelerated environmental resistance test were conducted on the disc prepared by the above method in the same manner as in Example 1. Figure 4 shows the relationship between the value of X in the composition of the Ti-3n-Se alloy film and the CN ratio obtained in the recording/reproduction test, and Figure 5 shows the relationship between the value of X and the bite error rate after the accelerated environmental resistance test. Indicates the relationship between From the results of this example, Ti-Sn-Se
It can be seen that good recording and reproducing characteristics and reliability can be obtained when the value of X in the composition of the alloy film is in the range of 25 to 100.

Example 3 A Ti-Sn-Se alloy film,
A 5n-Se alloy film and a Ti-3n-Se alloy film were sequentially laminated. At this time, the composition of the Ti-5n-3e alloy film is T ji
o (SnsiSess) io and the film thickness was changed.

A recording/reproducing test and an accelerated environmental resistance test were conducted on the disc prepared by the above method in the same manner as in Example 1. FIG. 6 shows the relationship between the thickness of the Ti-5n-3e alloy film and the CN ratio obtained in the recording/reproducing test. The results of this example show that good recording and reproducing characteristics can be obtained when the thickness of the Ti-5n-Se alloy film is 6 nm or less.

〔Effect of the invention〕

As is clear from the above description, by configuring the recording film as in the present invention, it is possible to obtain a recording film for a write-once optical disc that has good recording and reproducing characteristics and is highly reliable.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the layer structure of an optical recording medium according to the present invention, FIG. 2 is an explanatory view showing the relationship between recording power and CN ratio in Example 1 and Comparative Example 1, and FIG. An explanatory diagram showing the relationship between the accelerated deterioration test time and the bite error rate of the medium in Example 1 and Comparative Example 1, and Figure 4.5 shows the composition of the Ti-3n-Se alloy film and CN in Example 2, respectively.
FIG. 6 is an explanatory diagram showing the relationship between the thickness of the Ti-3n-3e alloy film and the CN ratio in Example 3. In the figure, 1: substrate, 2: portion where the content of passive state-forming metal is higher than the average passive state-forming metal content of the recording film,
3: Portion that does not contain or has a low content of passive state-forming metals. Figure 1 1... Substrate 2... Portion where the content of passive metal forming metal is higher than the average passive metal forming content of the recording film 3... Portion containing no passive metal or having a small content

Claims (1)

[Scope of Claims] 1. An optical recording medium comprising a substrate and a recording film containing at least one element selected from the group consisting of Sn, Bi, and Sb, Se, and a passive state-forming metal element, the recording film comprising: Optical recording characterized by having a portion near the interface with the substrate, near the surface on the opposite side, or both, where the content of the passive state forming metal is higher than the average content of the passive state forming metal element of the recording film. Medium. 2. The portion containing the passive state-forming metal element is limited to the vicinity of the interface between the recording film and the substrate, the vicinity of the surface on the opposite side, or both, and no passive state-forming metal element is contained inside these areas. An optical recording medium according to claim 1, characterized in that: 3. The light according to claim 1, wherein the content of the passive state-forming metal element in the portion with a high content of the passive state-forming metal element is in the range of 25% or more and 100% or less in terms of atomic percent. recoding media. 4. Claims 1 to 3, characterized in that the thickness of the portion containing the passive state-forming metal element is 6 nm or less
Optical recording medium described in Section 1. 5. The optical recording medium according to claim 1, wherein the passive state forming metal is Ti or Cr.