JPH0481955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium on which information can be recorded and reproduced using laser light, and a method for manufacturing the same.

(Prior Art) Optical disk memories, which record and reproduce information on a medium using laser light, have excellent characteristics as large-capacity recording devices because of their high recording density.
Tantalum and lead were first used as materials for this optical recording medium (Science 154,
1550, 1966)). Since then, various materials have been used, but chalcogen elements such as Te or compounds thereof are often used (Japanese Patent Publication No. 47-26897).
In particular, tellurium selenium alloys are often used (Special Publications 1984-41902, 1984-7919, 1983-
56058). In recent years, in order to downsize recording devices, semiconductor lasers have been used as laser light sources. Semiconductor lasers have an oscillation wavelength of around 8000 Å, and tellurium selenium alloys are relatively well suited to this wavelength range, and can provide moderate reflectance and moderate absorption (Physica Status Solidi (phys.stat)). .sol.7, 189, 1964)).

(Problems to be Solved by the Invention) However, none of these media satisfies all of the requirements of weather resistance, sensitivity, and signal quality.

An object of the present invention is to provide an optical recording medium that has good weather resistance, high sensitivity, good signal quality, and a large recording power margin, and a method for manufacturing the same.

(Means for solving the problem) An optical recording medium and a method for manufacturing the same according to the present invention are an optical recording medium for recording and reading information using a laser beam, and a method for manufacturing the same. The recording film is composed of a composite film whose main components are tellurium, selenium, and nitrogen. An optical recording medium characterized by comprising a film with a high nitrogen concentration, comprising a step of forming a film whose main components are tellurium, selenium, and nitrogen, and a step of forcibly nitriding the surface layer of this film. A method of manufacturing an optical recording medium is characterized in that:

(Operation) The optical recording medium has a structure as shown in the figure. That is, the recording layer 21 is provided on the substrate 1.
The recording laser beam is focused and irradiated onto the recording layer 21 through the substrate 1, and pits 22 are formed. As the substrate 1, synthetic resins such as polycarbonate, polyolefin, polymethylpentene, acrylic, and epoxy resins, and glass are used. Guide grooves are provided on the substrate so that pits are recorded concentrically or spirally at regular intervals with high precision. When light enters a groove with a width similar to the diameter of the laser beam, the light is diffracted, and as the beam center shifts from the groove, the spatial analysis of the diffracted light intensity changes.This is detected and the laser beam is directed to the center of the groove. The servo system is configured as follows. The width of the groove is usually
The depth of the groove is 0.3 to 1.3 μm, and the depth of the groove is set in the range of 1/12 to 1/4 of the wavelength of the laser used. A servo system is similarly configured for condensing light. Information is read by irradiating a laser beam with a weaker power than during recording so as to pass over the pits, and detecting changes in reflectance caused by the presence or absence of pits. Various materials can be used for the recording layer 21. Among them, tellurium has relatively good recording and reproducing properties. However, it could not be put to practical use because of severe oxidative deterioration in high-temperature, high-humidity environments. Also, the sensitivity was somewhat insufficient. 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 the sensitivity (Japanese Patent Application Laid-Open No. 58-58250). The inventors repeated this example to fabricate an optical recording medium and evaluated the recording and reproducing characteristics. Since there was almost no absorption, the sensitivity was insufficient. Furthermore, since nitrogen is easily liberated, the storage stability in a high temperature and high humidity environment was not sufficient. Furthermore, instead of forming a film by sputtering in nitrogen gas as proposed above, it has also been proposed to form a film by sputtering in a mixed gas of argon and nitrogen (Applied Physics Letters). Appl.Phys.Lett,
45, 202, 1984)). However, even with this, sufficient recording sensitivity and sufficient signal quality could not be obtained. By sputtering a tellurium selenium alloy target with a mixed gas of argon and nitrogen, the present inventors have obtained an optical recording medium with a recording layer composed of tellurium, selenium, and nitrogen, which has good weather resistance, high sensitivity, and good signal quality. We have already proposed this (Patent Application No. 101368, 1983). The reason why this recording layer has good weather resistance, high sensitivity, and good signal quality is as follows.
The addition of selenium lowered the melting point of the entire system, and the explosive properties of selenium nitride and tellurium nitride combined to cause the formation of small holes and expansion of pores due to surface tension to occur at relatively low temperatures. It seems that the sensitivity has been increased, and that the interaction between tellurium, tellurium nitride, selenium, and selenium nitride has a favorable effect, improving weather resistance and improving signal quality.

The present invention further improves this, and by forcibly nitriding the recording film of a film whose main components are tellurium, selenium, and nitrogen, and its surface layer to form a composite film with a high nitrogen content, it has improved weather resistance. It has high sensitivity, good signal quality, and has a large recording power margin. The reason why the margin of recording power increases is not yet fully clear, but it is thought that the formation of a layer with a high melting point on the surface of the recording film prevents pits from expanding as much during recording.

(Example) Examples of the present invention will be described below.

A polycarbonate resin disc substrate with an inner diameter of 15 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm (groove width 0.7 μm, groove depth 600 Å) annealed for 2 hours at 100°C is coated with 80:20 tellurium selenium in atomic percent. By magnetron sputtering the target using a mixed gas of argon and nitrogen with a nitrogen gas partial pressure of 4%, a film with a thickness of about 250 Å of tellurium, selenium, and nitrogen in an atomic ratio of approximately 77:19:4 was fabricated. did.
After that, nitrogen gas is introduced into a parallel plate electrode type plasma reactor and discharged to generate nitrogen plasma, and this plasma forms a nitrogen-rich layer with a nitrogen content of about 10% in atomic percent and a thickness of about 20 Å. An optical recording medium was fabricated using this composite film as a recording film.

The reflectance of the grooves of this optical disk was measured at a wavelength of 8300 Å with the substrate incident on it, and found to be approximately 29%.
Semiconductor laser light with a wavelength of 8300 Å is incident through the substrate and focused onto the recording film to approximately 1.6 μmφ, and the medium linear velocity is
5.65m/sec, recording frequency 3.77MHz, recording pulse width
Recording was performed in the groove under conditions of 70 nsec and recording power of 6.5 mW, and reproduction was performed at a constant power of 0.7 mW. Bandwidth
The carrier to noise ratio (C/N) at 30kHz is
A good value of 51dB was obtained. In addition, evaluation was performed using a bit error rate measurement method that sets a fixed slice level for the zero level of the AC playback signal and determines whether or not recording and playback was performed normally for each pit. As a result, a bit error rate of 10 ^-6 was obtained. Even when the recording power was set to 6.0 mW and 7.0 m, the bit error rate was similarly good at 10 ^-6 , confirming that there was a large margin of recording power.

Even after this optical disk was stored for 750 hours in a high temperature and high humidity environment at 80°C and 90%, the above characteristics did not change in practical terms, confirming that it is an optical recording medium with excellent weather resistance. The thickness of the layer mainly composed of tellurium, selenium, and nitrogen is preferably in the range of 100 Å to 1000 Å from the viewpoint of recording and reproducing characteristics, and 200 Å is particularly desirable.
It is 400Å from The content of selenium is desirably in the range of 2% or more and less than 40% in terms of atomic percent from the viewpoint of recording/reproducing characteristics, weather resistance, and unrecorded noise, and it is particularly desirable to have a selenium content of 10% or more.
Less than 30%. The content of nitrogen is desirably 2% or more and less than 20% in terms of atomic percent from the viewpoint of recording and reproducing properties and weather resistance, and particularly preferably 2% or more and less than 10%. The content of nitrogen in the recording film depends not only on the sputtering target composition ratio and nitrogen gas partial pressure, but also on the size of the sputtering device (surface area of the sputtering chamber, etc.), sputtering time, etc. Therefore, the nitrogen gas partial pressure at which the optimum composition can be obtained cannot be determined uniquely, and it is necessary to appropriately set the nitrogen gas partial pressure for each sputtering device.
The layer mainly composed of tellurium selenium and nitrogen contains lead,
Antimony, arsenic, sulfur, tin, germanium, thallium, phosphorus, cadmium, indium,
Gallium, zinc, bismuth, aluminum, copper,
silver, magnesium, tantalum, gold, palladium,
Addition of at least one element selected from the group of cobalt may improve the shape of the pit. However, the amount added is preferably less than 20% in atomic percent.

This example will be explained below.

A polycarbonate resin disk substrate with a guide groove having an inner diameter of 15 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm, which had been annealed at 100° C. for 2 hours, was placed in a magnetron sputtering device equipped with a 13.56 MHz high-frequency power source, and the air was evacuated. After evacuation to below 2×10 ^-6 Torr, argon gas and nitrogen gas were introduced to bring the pressure to 1×10 ^-2 Torr.
At this time, the nitrogen gas partial pressure was 0.26%, and the nitrogen gas flow rate was 0.30 SCCM. Atoms of tellurium, nitrogen, selenium, and lead were sputtered on an 8-inch target made of a sintered body of tellurium selenium lead alloy with a ratio of 73:20:7 at % by using this mixed gas at an input power of 120 W while rotating the disk substrate. A film with a thickness of approximately 220 Å with a number ratio of approximately 71:2:20:7 was fabricated.
Thereafter, a layer with a high nitrogen content of 6 atomic % and a thickness of about 20 Å was formed on the surface by the same treatment as in the above example, and then placed in an environment at a temperature of 85° C. and a relative humidity of 90%. After storage for 12 hours, an optical recording medium made of a polycrystalline film was fabricated.

When we measured the reflectance of this optical disk incident on the substrate at a wavelength of 8300 Å, it was approximately 32%. Semiconductor laser light with a wavelength of 8300 Å is incident through the substrate and focused on the recording layer to approximately 1.6 μmφ, and the medium linear velocity is
5.65m/sec, recording frequency 3.77MHz, recording pulse width
Recorded under the conditions of 70nsec and recording power 6.0mW, 0.7
Regeneration was performed at mW. The carrier-to-noise ratio (C/N) with a bandwidth of 30 kHz was good at 49 dB.
This value was sufficiently stable for practical use even against fluctuations in recording power caused by changing the recording/reproducing device. After storing this optical disk in a high temperature and high humidity environment at 85° C. and 90% for 200 hours, the above characteristics were examined, but there were no changes, confirming that the optical recording medium had excellent weather resistance. Under these conditions, the bit error rate does not change in the recording film that does not contain lead, but protrusions of about 0.01 to 0.1 μm occur on the film surface, but these do not occur in the recording film that contains lead. do not. This inhibitory effect could not be obtained with a lead content of 5 atomic % or less. When a recording film was prepared by sputtering a tellurium selenium lead target without introducing nitrogen gas, the recording sensitivity was unstable and was insufficient for practical use.

Forced nitriding can be performed with good controllability by introducing a nitrogen-containing gas such as N ₂ gas into a plasma reactor having cylindrical or parallel plate electrodes and causing discharge. It is particularly desirable for the thickness of the forced nitrided film to be in the range of 10 Å to 100 Å, since this allows for a large margin of recording power without deteriorating the recording/reproducing characteristics.

(Effects of the Invention) As is clear from the above embodiments, the present invention provides an optical recording medium with good weather resistance, high sensitivity, good signal quality, and a large recording power margin, and a method for manufacturing the same.

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view showing an example of an optical recording medium. In the figure, 1 is a substrate, 21 is a recording layer, 22
represents pit.

Claims (1)

[Scope of Claims] 1. An optical recording medium for recording and reading information using a laser beam, comprising a recording film formed on a substrate and consisting of a composite film mainly composed of tellurium, selenium, and nitrogen, and comprising the above-mentioned A composite film containing tellurium, selenium, and nitrogen as main components is characterized by comprising a first film containing tellurium, selenium, and nitrogen as main components, and a second film having a higher nitrogen concentration than the first film. optical recording medium. 2. A method for manufacturing an optical recording medium in which information is recorded and read by laser light, comprising the steps of forming a film containing tellurium, selenium, and nitrogen as main components, and forcibly nitriding the surface layer of this film. A method for manufacturing an optical recording medium, characterized in that: