JPH02171285A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent generation of protrusions on the surface of film and make possible maintenance of medium properties in satisfactory condition even if it is stored in environments of high temperature and humidity by providing a crystalline recording layer consisting mainly of tellurium, selenium, lead, nitrogen and oxygen. CONSTITUTION:A substrate 1 is formed as an injection-molded polycarbonate resin disk substrate with a guiding groove. After the substrate 1 is annealed as specified, it is installed in a magnetron sputtering device with a high frequency power supply and the gas is exhausted. Next, after this exhaustion, argon and nitrogen gases are introduced and a film of specified thickness is formed on the substrate 1 by sputtering a sintered target of tellurium, selenium and lead alloy with a specifically charged power. After this, the recording layer 2 consisting of tellurium, selenium, lead and nitrogen layers is crystallized by keeping it under circumstances of specified high temperature and humidity. Then a crystal particle field is oxidized to obtain an optical recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical recording medium such as an optical disk on which information can be recorded and reproduced using laser light.

[Prior Art] Conventionally, as this type of technology, there is an optical disk memory that records and reproduces information on a medium using laser light.
Because of its high recording density, it has excellent characteristics as a large-capacity recording device. Initially, tantalum and lead were used as materials for this optical recording medium (Science).
ence) 154, 1550.1966), various materials have been used since then, but chalcogen elements such as tellurium or their compounds are generally often used (Japanese Patent Publication No. 47-26897), and among them, Tellurium-selenium alloys are particularly commonly used (Japanese Patent Publications No. 41902/1982, 7919/1982, and 5Ei058/1983).This tellurium-selenium alloy is used as an optical recording layer. An example of a conventional optical recording medium has a structure as shown in FIG. That is, on the surface of the substrate 11, a recording layer 21 made of a tellurium-selenium alloy is formed. In the recording layer 21, pits 22 are formed by condensing and irradiating a recording laser beam through the substrate 11. As the substrate 11, polycarbonate, polyolefin, polymethylpentene, acrylic,
Synthetic resins such as epoxy resins and glass are used. Further, guide grooves are usually provided on the substrate 11 so that the pits 22 are recorded concentrically or spirally at regular intervals with high accuracy.

In such an optical disk memory, when light enters a groove having a width approximately the diameter of a laser beam, the light is diffracted, and as the beam center deviates from the groove, the spatial distribution of the intensity of the diffracted light changes. A servo system is configured to detect this and direct the laser beam to the center of the groove. The width of the groove is usually 0.3 to 1.3 gm, and the depth of the groove is set in the range of 1720 to 1/4 of the laser wavelength used.

A servo system is similarly configured for condensing light.

Information is read from the optical disk memory by irradiating a laser beam with a power weaker than that used during recording so as to pass over the bits, and detecting changes in reflectance caused by the presence or absence of pits.

Note that in order to downsize recording devices, semiconductor lasers have been used as laser light sources. Semiconductor lasers have an oscillation wavelength of around 8,000 nm, and tellurium-selenium alloys are relatively well suited to this wavelength range, and can provide moderate reflectance and moderate absorption (Physica Fistitus Nridai, 7). , 189, 11164 (phys-stat
-sol-7,189,19f14) ).

The above-mentioned tellurium-selenium alloy has relatively good recording and reproducing characteristics. However, it cannot be put to practical use because of severe oxidative deterioration in high-temperature, high-humidity environments, and it also has the disadvantage of being somewhat insufficient in sensitivity. Therefore, as one solution to the lack of sensitivity, it has been proposed to include nitrogen in the tellurium film so that nitrogen is liberated during heating and increases sensitivity (Japanese Patent Application Laid-open No. 57-58250). They fabricated an optical recording medium based on this example and evaluated the recording and reproducing characteristics, and found that the semiconductor laser wavelength (approximately 8300
In humans, there is almost no absorption, resulting in insufficient sensitivity. or,
Since nitrogen is easily liberated, storage stability in high temperature and high humidity environments is not sufficient.Also, instead of forming a film by sputtering in nitrogen gas as proposed above, sputtering is performed in a mixed gas of argon and nitrogen. It has also been proposed to form a film by applying the same method (Applied Physics Reference CAppI-Phys-Lett, 45, 202.
1984) ).

However, even with this, it is still difficult to obtain sufficient recording sensitivity and sufficient signal quality.

For this reason, the present inventors developed a recording layer consisting of tellurium, selenium, and nitrogen by sputtering a tellurium selenium alloy target with a mixed gas of argon and nitrogen, thereby achieving optical recording with good weather resistance, high sensitivity, and signal quality. He discovered that a medium could be obtained and has already proposed it (patent application 1986-10).
1388).

[Problems to be Solved by the Invention] However, in the conventional optical recording medium described above, the recording layer is formed of tellurium, selenium, and nitrogen, and although it is not satisfactory in terms of weather resistance and sensitivity, The optical recording medium is placed in a high temperature and high humidity environment with a temperature of 85°C and a humidity of 90%.
After 00 hours of storage, there is no change in the pit error rate of the stored data, but the recording sensitivity changes, and the film surface has 0.01
There is a drawback that granular protrusions of about 0.0, IILm are generated.

[Means for Solving the Problems] The recording medium of the present invention has been made to solve the above-mentioned conventional problems, and includes a substrate, a portion of which is formed on the substrate, and a portion of which is selected by a laser beam. In an optical recording medium having a recording layer from which information is recorded by removing the information, the recording layer is made of a crystalline material whose main components are tellurium, selenium, lead, nitrogen, and oxygen.

[Examples] Examples of the present invention will be described below with reference to the drawings.

Fig. 1 is a partial sectional view showing one embodiment of the present invention, Fig. 2 is a partial sectional view showing the second embodiment, Fig. 3 is a partial sectional view showing the third embodiment, and Fig. 4 is a partial sectional view showing the third embodiment. FIG. 5 is a diagram showing the characteristics when the selenium content is changed in the first example, and FIG. 5 is a diagram showing the characteristics when the lead content is changed in the first example.

An optical disk is taken as an example of the optical recording medium of the first embodiment. This optical disc basically consists of a substrate 1 and a recording layer 2.
It consists of

The recording layer 2 is made of a crystalline material whose main components are tellurium, selenium, lead, nitrogen, and oxygen.

Next, a method for manufacturing the optical disc of the first embodiment will be explained.

First, the board 1 has an inner diameter of 15 layers and an outer diameter of 130 m.

Formed as an injection molded polycarbonate resin disc substrate with guide grooves 1.21 mm thick. And the board 1t7
After annealing at t100℃ for 2 hours, 13.56M
It is installed in a magnetron sputtering device having an H7 high frequency power source and evacuated.

Next, after exhausting to 2X IO-'Torr or less, argon gas and nitrogen gas were introduced, and 5X 10-3T
orr. The nitrogen gas partial pressure at this time was 0.35%.

The nitrogen gas flow rate was 0.3 B'; CCN. Then, by sputtering an 8-inch target made of a sintered body of tellurium selenium lead alloy with an atomic percent ratio of 73:20:7 using this mixed gas at an input power of 150 W, approximately 2.
A film having a thickness of 40 mm is formed on a substrate 1 which is a disk substrate.

Thereafter, the recording layer 2 consisting of the tellurium-selenium-lead-nitrogen layer was stored for 12 hours in an environment at a temperature of 85° C. and a relative humidity of 90%.
An optical recording medium is manufactured by crystallizing and oxidizing the grain boundaries.

When each characteristic of this recording layer 2 was analyzed, the following results were obtained.

First, the atomic ratio of tellurium, selenium, lead, nitrogen, and oxygen was approximately 64:18:6:1:11.

Further, the reflectance of the land portion of this optical disk at a wavelength of 83 OO was approximately 31% when the light was incident on the substrate.

Also, the carrier-to-noise ratio (
C/N value). At this time, a semiconductor laser beam with a wavelength of 8300A is incident on the recording layer through the substrate.
．． Narrow down to about mφ, medium linear velocity 5, 65s/sec
, recording frequency 3.77MHz, recording pulse width 70ns
ea, recorded on the land section under the conditions of recording power 5.4W,
It is assumed that reproduction is performed at a constant power of 0.7 layer W. As a result, a good C/N value of 50 dB was stably obtained. This value was stably obtained even when a large number of optical disks were measured. Furthermore, stability was obtained even against fluctuations in recording power caused by changing the recording/reproducing device.

Next, a fixed value slice level is set for the zero level of the reproduced signal, and evaluation is performed using a bit error rate measurement method that determines whether recording and reproduction have been performed normally for each bit 3. . As a result, a stable bit error rate on the order of 10-6% was obtained for a large number of optical discs.

Next, when this optical disk was stored in a high temperature and high humidity environment of 85° C. and 90% humidity, it was confirmed that no granular protrusions were generated on the film surface.

At this time, 1.
Sensitivity characteristics recorded after storage for 000 hours.

The bit error rates were examined, and it was confirmed that there was no change in practical use.

Next, the results of a characteristic test based on changes in the thickness of the recording layer 2 and the ratio of each component are shown below.

The thinner the recording layer 2 is, the higher the sensitivity becomes, but the rim formed around the bit 3 becomes discontinuous, resulting in increased noise, lower reflectance, and smaller carriers. For this reason, a good C/N value cannot be obtained. On the other hand, if the recording layer 2 is made thicker, the recording sensitivity deteriorates and the amount of recording layer material that is melted and removed from the irradiated area increases, so the rim is not formed uniformly and the C/N value decreases.

Therefore, the thickness of the recording layer 2 is preferably in the range of 160A to 400A.

Characteristic changes in the composition ratio of each component of the recording layer 2 are as follows.

The effect of changing the content of selenium and lead was tested by changing the composition of the sputtering target. The ratio of tellurium, selenium, and lead in the recording layer 2 produced at this time was approximately equal to the ratio of tellurium, selenium, and lead in the sputtering target.

Figure 4 shows the characteristics when the selenium content is changed.

When the selenium content is too low, corrosion occurs when stored in a high temperature and high humidity environment for a long time. On the other hand, if there is too much selenium, unevenness on the order of microns will occur and unrecorded noise will become large, making it impossible to put it into practical use. Therefore, the selenium content is 9 atomic%.
% or more and less than 35%.

Figure 5 shows the effect of suppressing granular protrusions under storage in a high temperature and high humidity environment when the lead content is varied. The content is preferably 5 at% or more, however,
If the lead content is too high, the medium properties will deteriorate after being stored in a high temperature and high humidity environment for a long time, so the lead content is preferably 15 at % or less.

It should be noted that microscopic granular protrusions that occur when stored in a high-temperature, high-humidity environment for a long time are different from the conventional tellurium-selenium-lead-nitrogen (
The reason why this occurs in the recording layer 2 consisting of (-oxygen) and can be suppressed by containing lead is considered to be as follows. In a high temperature, high humidity environment, tellurium selenium is easily ionized and moves, resulting in the generation of granular protrusions; however, when lead is added, the mobility of these ions decreases, thereby suppressing the generation of granular protrusions. It is.

Note that the degree of generation of granular protrusions is smaller when nitrogen is included than in a recording film made of tellurium-selenium-lead (-oxygen).

Next, an experiment was conducted regarding the nitrogen content by changing the nitrogen gas partial pressure.

Recording layer 2 with a low nitrogen content has poor recording sensitivity.
Further, it was not possible to record uniformly over one lap of the track, and some pits 3 were observed to be missing.

Therefore, the pit error rate is very bad and the C/N value is also bad.On the other hand, if you increase the recording power, you may be able to obtain a good C/N value. However, if you increase the recording power further, the tracking servo will malfunction, so it is important to have enough recording power. The degree is very narrow and cannot be used for practical purposes. At this time, even when a good C/N value is obtained, pit 3 is partially missing and the pit error rate is poor.The reason for this is that tellurium-selenium-lead (-
This is because although the melting point of the (oxygen) film is low, it is difficult to form small holes in the irradiated melted part, making it difficult for pits to open, and therefore, a large recording power is required to form bits.

In addition, since a large recording power is applied, the area of the melted portion becomes large, and when the -degree bit 3 opens, it becomes a large dot 3, making it easy for the tracking servo to malfunction.

When part of tellurium and selenium is nitrided as in the optical recording medium of this example, small holes are easily and stably formed in the irradiated melted part due to the explosive nature of tellurium nitride and selenium nitride, resulting in a decrease in recording sensitivity. The pit error rate is small because there are no missing pits.

Furthermore, since the pits 3 open without melting over a large area, the pits 3 do not become very large, so there is no tracking servo malfunction.

However, if the nitrogen content is too high, the surface properties of the film will deteriorate, and the rims around the pits will not be formed neatly, resulting in increased noise after recording, making the film impractical.

Furthermore, if the nitrogen content is further increased, although there is absorption at the argon laser wavelength (around 5,000 λ), it is absorbed at the semiconductor laser wavelength (around 8,000 λ), which is the light source of small recording devices.
This results in a film with almost no absorption. Therefore, the nitrogen content is desirably 0.5% or more and 10% or less in atomic %.

Furthermore, the inclusion of oxygen in the recording layer 2 increases the margin of recording power and is also effective in preventing changes in recording sensitivity even after long-term storage in a high-temperature, high-humidity environment.

However, if the oxygen content is too low, the margin of recording power and the recording sensitivity will deteriorate, and if it is too high, the recording sensitivity will decrease and a rim with a good shape will not be formed, resulting in a decrease in the C/N value.

Therefore, it was confirmed that a good effect is obtained when the oxygen content is in the range of about 5% to 25% in atomic percent.

As described above, in the first embodiment, by using a crystalline recording film whose main components are tellurium, selenium, lead, nitrogen, and oxygen, the generation of protrusions on the film surface can be suppressed. .

Further, as the recording layer 2 of this example, tellurium-selenium-
A polycrystalline film of lead-nitrogen is used, the grain boundaries of which are oxidized.

By making the recording layer 2 polycrystalline, the pits 3
Since the formation of small holes when the recording layer 2 is in a solution state, which is the initial stage of the formation mechanism, occurs easily and stably, the recording sensitivity is stabilized. Furthermore, since the material is polycrystalline, the expansion of the small hole is likely to be inhibited by grain boundaries, making it difficult to expand more than necessary, resulting in a greater margin of recording power.

On the other hand, the purpose of oxidizing the grain boundaries is to further ensure the recording sensitivity and weather resistance effects obtained by making the film polycrystalline.

In this example, the recording layer 2 was formed directly on the substrate l, but the recording layer 2 may be formed after forming a base layer on the upper surface of the substrate l in advance. An optical disc having a geological layer will be explained.

In the second embodiment of the present invention, as shown in FIG. 2, 3,4,9.10-perylene tetracarboxylic dianhydride (hereinafter referred to as PTODA) is used as the underlayer 3.

Next, the manufacturing method will be explained.

A base layer 3 made of PTCDA is formed to a thickness of about 100 mm on a polycarbonate resin disk substrate, which is a substrate 1 similar to that shown in FIG. Next, on this base layer 3, tellurium-selenium-
A lead alloy target is formed to a thickness of approximately 240 mm by magnetron sputtering using a mixed gas of argon and nitrogen. After that 7
Store tellurium-selenium in an environment of 0℃90% for 24 hours
The recording layer 2 of the tellurium-selenium-lead-nitrogen-oxygen layer is formed by crystallizing the lead-nitrogen layer and oxidizing the grain boundaries.

Next, the results of analyzing the characteristics of the second example will be shown.

At this time, the atomic ratio of tellurium, selenium, lead, nitrogen, and oxygen is approximately 64:18:6:1:11, the same as in the first embodiment.
Met.

When the reflectance of the land portion of the substrate was measured under the same conditions as in the first example, it was approximately 28%.

In addition, the band [30KHz carrier-to-noise ratio (
A good value of 48 dB (C/N value) was stably obtained under the same conditions as in the first example. This value is obtained stably even when measuring a large number of optical disks, and is obtained stably even with recording power fluctuations caused by changing the recording/playback device. When evaluated, it was stable with a large number of discs, and the performance was about 10 as in the first embodiment.
A bit error rate of -6% was obtained.

Further, the standard deviation of the variation in recording sensitivity is approximately 0.2 mW in the absence of the PTODA underlayer 3. On the other hand, in this example, it was approximately 0.1 mW, and it was confirmed that the variation in recording sensitivity was reduced.

The thickness of the base layer 3 made of PTCDA is preferably in the range of 5 to 100A.

Note that the thickness of the recording layer 2 and the composition ratio of each component are the same as in the first embodiment.

In the second embodiment, by providing the PTCDA underlayer 3, variations in recording sensitivity can be reduced. The reason for this is thought to be as follows. In the case where the recording layer 2 is directly attached to the substrate 1 as in the first embodiment, recording is performed in the same interface state over the entire substrate surface and on all substrates due to process variations in the pre-processing process for the substrate 1. It becomes difficult to form layer 2. Therefore, in this embodiment, P
Since the TCDA base layer 3 and the recording layer 2 are formed continuously, the adhesion state between the recording layer 2 and the base layer 3, which has the greatest effect on variations in recording sensitivity, is not affected by the pre-film formation process. , there is no variation in recording sensitivity. In addition, base layer 3
The reason why PTODA was selected as the material is that since PTCDA decomposes at the temperature at which the recording layer 2 is melted by laser irradiation, it ensures the formation of small holes, which is the initial stage of the bit formation mechanism.

A third embodiment of the present invention in which antimony oxide is used as the base layer 4 will be described below.

Next, the manufacturing method will be explained.

An underlayer 4 made of antimony oxide (Sb20s) is formed to a thickness of about 24 OA on a polycarbonate resin disk substrate 1 similar to that of the first embodiment. Subsequently, a tellurium-selenium-lead alloy target was magnetron sputtered onto the base layer 4 using a mixed gas of argon and nitrogen to give an approximately 24O
Form A thickness. 121I in an environment of 85°C and 90%
to crystallize the tellurium-selenium-lead-nitrogen layer,
By oxidizing the grain boundaries, the recording layer 2 of tellurium-selenium-lead-nitrogen-oxygen layer is formed.

Next, the results of analyzing the characteristics of the third example will be shown.

The atomic ratio of tellurium, selenium, lead, nitrogen, and oxygen was approximately 64:18:6:1:11, as in the first example.

When the reflectance of the land portion of the optical disk substrate was measured under the same conditions as in the first embodiment, it was approximately 29%.

Also, the carrier to noise ratio (C
/N value) was stably obtained at a good value of 48 dB. This value was stably obtained even when a large number of optical disks were measured, and was stably obtained even when the recording power fluctuated due to changing the recording/reproducing device.

Next, when similarly evaluated using the bit error rate measurement method,
A bit error rate of approximately 10-6% was stably obtained with a large number of optical disks, similar to the first embodiment.

The variation in recording sensitivity was approximately 0.1 fat W, and it was confirmed that the variation in recording sensitivity was reduced. This is the same value as in the second embodiment.

In addition, the thickness of the antimony oxide layer ranges from 5 to 25
A range of 0OA is desirable.

Further, the thickness and composition ratio of the recording layer 2 are the same as in the first embodiment.

In this embodiment, by providing the antimony oxide underlayer 4, variations in recording sensitivity can be reduced. The reason for this is that the antimony oxide underlayer 4 and the recording layer 2 are formed continuously, similar to the second embodiment. Since the adhesion state between the recording layer 2 and the underlayer 4, which has the greatest influence on variations in recording sensitivity, is not affected by the pre-film formation process, variations in recording sensitivity are eliminated. Furthermore, antimony oxide was used as the underlayer 4 because antimony oxide decomposes at the temperature at which the recording layer 2 melts when irradiated with a laser, thereby ensuring the formation of small holes, which is the initial stage of the pit formation mechanism. It is.

Note that in the second and third embodiments, a PTCDA layer and antimony oxide were used as the base layer 3.4;
If it is something that reduces the variation in recording sensitivity,
Of course, it is also possible to use something else.

[Effects of the Invention] As explained above, the optical recording medium of the present invention has improved weather resistance and signal quality by making the recording layer a crystalline material whose main components are tellurium, selenium, lead, nitrogen, and oxygen. Also, there is an effect that the recording power margin is improved and the sensitivity is increased.

Furthermore, even when stored in a high temperature, high humidity environment for a long time, the generation of protrusions on the surface of the film as in the prior art can be prevented and the medium properties can be maintained favorably.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing an embodiment of the optical recording medium of the present invention, FIG. 2 is a partial cross-sectional view showing a second embodiment of the present invention,
FIG. 3 is a partial sectional view showing a third embodiment of the present invention;
The figure shows the characteristics when the selenium content rate is changed in the first example. Figure 5 is a graph showing the characteristics when the lead content rate is changed in the first example. It is a partial sectional view of a conventional example. l Two substrates 2: Recording layer 3: Pit
4: PTCDA layer 5 antimony dioxide layer Figure 1

Claims (1)

[Claims] An optical recording medium comprising a substrate and a recording layer formed on the substrate and recording information by selectively removing a portion with a laser beam, wherein the recording layer is made of tellurium. An optical recording medium characterized by being made of a crystalline material whose main components are selenium, lead, nitrogen, and oxygen.