JPH0447382B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium capable of high-density, high-speed recording.

Specifically, the present invention relates to an optical recording medium that utilizes the fact that a thin recording film formed on a base material is evaporated or melted away by heat generated by irradiating the thin film with a laser beam.

(Prior art) Metal thin films such as Te and Bi have traditionally been used as optical recording media in which holes (pits) are formed by irradiating a thin film formed on a substrate with a laser beam. It has been known. In order to further increase the stability over time, Te consisting of Te, Se, etc.
The use of alloy thin films and plasma polymerized films containing these metals is also being considered. Since these materials have a low melting point, the power of the laser beam required for recording is small, which is advantageous in terms of recording sensitivity.

On the other hand, substrates used for these recording media include plastic, glass, metal, and substrates coated with photocurable resin.

In the above-mentioned system consisting of a substrate and a thin film recording medium, in order to perforate the thin film recording layer with a laser beam, it is necessary that the recording layer material melted by laser heating be separated by the adhesive force with the substrate. For this purpose, it has been considered to provide an undercoat layer made of a thin fluorocarbon film between the recording layer and the substrate (Japanese Patent Application Laid-Open No. 1983-90246). The factors that determine the adhesion force are the surface tension of the substrate surface and recording layer material, the molecular weight of the substrate surface layer, the degree of crosslinking, etc., but if the adhesion force is small, pit holes can be formed in a short time with a smaller laser beam power. can do. This means improved recording sensitivity, enables high-speed recording, and allows the use of inexpensive low-power semiconductor lasers.
Furthermore, in order to perform high-quality recording, it is required that the formed pit shape have a clear outline and be uniform.

In order to meet the above requirements, the present inventors have already provided a fluorocarbon undercoat layer between the substrate and the recording layer, and the carbon of the layer within 10 nm from the surface of the undercoat layer in contact with the recording layer. We have discovered an optical recording medium in which the atomic ratio of fluorine and fluorine to 1 carbon is 1.4 or more as measured by ESCA (soft X-ray excitation photoelectron spectroscopy). (Special application 1986-
298197) (Problems to be Solved by the Invention) On the other hand, in addition to the above characteristics, a recording medium is required to have a large storage capacity, that is, to be capable of high-density recording. In order to improve the storage capacity of a punch-type optical recording medium, it is desirable to reduce the size of the pits as much as possible. High density using disc-shaped disk,
High-speed recording is achieved by shortening the irradiation time of the drilling laser beam, increasing the pulse repetition frequency, and reducing the spot size of the focused laser beam in the drive system that performs recording and playback.
Furthermore, this is accomplished by rotating the disk at high speed.

As the disc-shaped disk rotates and the laser beam spot moves relatively on the surface of the recording medium,
The pit length in the moving direction depends on the characteristics of the recording medium consisting of the recording layer and the undercoat layer, the spot size of the laser beam focused on the surface of the recording medium, the laser beam irradiation time, the intensity of the laser beam, and the laser beam. It is determined by the relative moving speed of the recording medium surface, etc. For optical systems generally used for optical recording and semiconductor laser light having a wavelength of around 800 nm, the laser light spot size is limited to a diameter of about 1 μm, and the shortest pit length is equal to or larger than this spot size. When the thermal conductivity of the recording medium is high and the area that is melted by laser beam irradiation is large, or when the adhesive force between the recording layer and the undercoat layer is too weak and a large amount of material is removed, , the shortest pit length that can be formed tends to be large. Also,
In the medium described above, the pit length tends to vary sensitively even with slight variations in laser light power, making it difficult to record stable and accurate digital signals.

Furthermore, in addition to the above-mentioned problems regarding the pit shape, when recording with short pulse length laser light or rotating the disk at high speed, the outer periphery of the disk may be irradiated per unit time per unit area on the medium surface. Since the energy density of the laser beam used for drilling becomes smaller, the power of the laser beam required for drilling becomes greater, and the demands for higher sensitivity of the medium become even more severe.

In order to meet the above requirements, the combination of the recording layer and its underlayer (substrate or undercoat layer) is an extremely important element. That is, in order to shorten the shortest pit length, it is desirable to have a large adhesive force, and on the other hand, in order to increase sensitivity, it is desirable to have a small adhesive force, which are seemingly contradictory demands that must be satisfied. To overcome this contradiction,
For example, a method of improving sensitivity by using organic substances (dyes such as nitrocellulose, guanine, or phthaloanine) that have high adhesion but decompose and sublimate at low temperatures as an undercoat layer (32nd Union of Applied Physics Proceedings of the conference (1985, Spring) p115), but sufficient sensitivity and stability are not necessarily obtained. Furthermore, the physical properties (decomposition/sublimation temperature, adhesion strength) of these existing organic materials are unique to each one, and cannot be flexibly optimized for combinations with various recording layers and drive systems.

(Means for solving the problem) On the other hand, when a recording layer is formed on a film of a copolymer of fluorocarbon and hydrocarbon and the recording sensitivity is measured, by increasing the ratio of fluorocarbon in the copolymer, It is possible to reduce the adhesion force and improve recording sensitivity (DJBroer and
L. Vriens appl phys A32 p107 (1983)) Conversely, it is known that plasma treatment of the surface of polytetrafluoroethylene resin improves its adhesion to metals and resins. (Reference J.Richard et−
al J.appl Polym Sci16 (1972) 1465) The present inventors focused on the good controllability of the adhesion force in such a fluorocarbon film, and as a result of various studies on the undercoat layer made of a thin fluorocarbon film, they found that the adhesion force could be improved. The present invention has been achieved by obtaining an optical recording medium having a fluorocarbon undercoat film that provides high sensitivity and improved pit shape while shortening the minimum pit length.

That is, the gist of the present invention is to provide an undercoat layer made of a fluorocarbon film on a substrate, and to form a surface of the fluorocarbon undercoat layer in an optical recording medium in which a perforated recording layer is disposed on the undercoat layer. It consists in inert gas plasma treatment.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing one example of the specific structure of the optical recording medium of the present invention, in which 1 is a substrate, 2 is a fluorocarbon subbing film disposed on the substrate 1, and 3 is a subbing film of fluorocarbon disposed on the film 2. The formed recording layer 4 is a groove for track servo.

The substrate 1 of the recording medium according to the present invention may be made of plastic such as acrylic resin or polycarbonate resin, glass, or aluminum coated with an ultraviolet curing resin.

In the present invention, a fluorocarbon thin film of 20 to 1000 Å, preferably 50 to 300 Å, is deposited on this substrate by plasma polymerization, sputtering, or vapor deposition.
After the fluorocarbon film is deposited, the surface of the fluorocarbon film is treated with inert gas plasma to form an undercoat layer 2, and the adhesion force with the underlying layer for various recording layers 3 is optimized.

When forming a fluorocarbon plasma polymerized film or a polyfluorocarbon sputter film 2 on the substrate 1, the fluorocarbon may include perfluoroalkanes such as CF ₄ and C ₂ F ₆ ;
Perfluoroalkenes such as CF ₃ CFCF ₂ , perfluorohexane, perfluorobenzene, etc.
Even if the fluorocarbon is a gas or liquid at room temperature, its vapor pressure is sufficiently high that it is difficult to store the vapor in a vacuum container.
It is desirable that the material satisfies 10 ^-3 Torr or more, enables glow discharge, and has a high degree of fluorine substitution.
A plasma polymerized film is formed by using these fluorinated carbons as monomers and using capacitive or inductive discharge. As the polyfluorocarbon, polytetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin, etc. are used, and these are used as targets for inert gas such as Ar, or , a sputtered film is formed by sputtering with a mixed gas of an inert gas and the monomer.

The recording layer 3 is usually made of Te-based alloy, especially Te alloy.
Te-Se alloys are good. To form a Te-Se recording layer, target Te or an alloy containing Te as a main component, and introduce selenium fluoride gas into a sputtering device to form a sputtered film. good. Inside the recording layer
The content of Se is preferably about 5 to 25 atomic %.

FIG. 2 shows an example of an apparatus for forming a recording layer by sputtering after a polyfluorocarbon sputtering film or plasma polymerized film is prepared and plasma-treated. In the figure, 1 is a vacuum container, the interior of which is divided into three chambers. For example, sputtering of polyfluorocarbon is performed in the first chamber, and then plasma treatment is performed in the second chamber. Thereafter, a recording layer is formed in the first chamber. Plasma treatment is
If the recording layer is an alloy containing Te, the average atomic ratio of fluorine to carbon in the layer within 10 nm from the surface of the fluorocarbon layer in contact with the recording layer is approximately 1.0 to 1.2 fluorine to 1 carbon. Better to process it.

In Fig. 2, 2, 3, and 4 are electrodes that apply high frequency waves, and they basically have the same structure, but 2 and 4 are targets made of the material to be sputtered, while 3 is a target made of the material to be sputtered. Materials that are difficult to damage (stainless steel, Ta, etc.) are used. Reference numeral 5 denotes a holder on which substrates 6 are set, and can be transported in order from chamber to chamber. Reference numerals 7, 8, and 9 are gas inlet ports for generating electric discharge, and the film forming chamber,
through 7 and 9 with Ar or reactive gas.
Introduce a gas mixture with Ar gas. For example, Ar gas is introduced into the plasma processing chamber through 8.
Here, between the chambers is a differential exhaust chamber 1 for independently controlling the type and pressure of gas in each chamber.
0 and 11 are provided. In addition, 12 is an exhaust port, 1
3 is an RF power supply. In the fourth chamber, if the material of the electrode 2 is changed to a material that is not easily spattered by plasma as in 3 and fluorocarbon monomer gas is introduced from the inlet 7, a plasma polymerized film can be produced.

In order to perform inert gas plasma treatment in the first chamber, glow discharge plasma is generated between the substrate holder 5 and the electrode 3, and the surface of the fluorocarbon film formed on the substrate 6 in the first chamber is exposed to the plasma. Just expose it.

Fluorine atoms are removed from the surface of the fluorocarbon film exposed to plasma, and carbon atoms are crosslinked, forming a highly crosslinked surface layer. The thickness and degree of crosslinking of the surface layer can be controlled by the plasma discharge conditions, particularly the discharge power, the treatment time exposed to the plasma, and the distance between the substrate 6 and the electrode 3, so that the recording layer and the undercoat layer are The adhesion force can be controlled over a wide range and optimized for various recording layers. In other words, by removing the fluorine atom,
The density and molecular weight of the surface crosslinked layer increase due to the increased surface tension of the fluorocarbon membrane surface and the crosslinking of carbon atoms. All of these changes in the surface layer have the effect of increasing the adhesion between the recording layer and the undercoat layer.

The effect of plasma treatment on the surface of a fluorocarbon thin film as described above was confirmed as follows.
First, a sputtered film of PTFE (polytetrafluoroethylene) was prepared, and then Ar gas pressure was
Ar plasma treatment was performed at 10 ^-3 Torr and discharge power of 100 W, and the contact angle with water and the atomic ratio of fluorine atoms to carbon atoms (F/C) in a layer within 10 nm from the surface were measured by ESCA method. The change in was measured. For measurement using the ESCA method, please refer to the patent application
60-298197.

It was confirmed that the contact angle and F/C decreased as the treatment time increased. On the other hand, Te
- When a SeF ₆ -based recording layer (disclosed in Japanese Patent Application No. 172,647) was formed and the adhesion force was measured by a simple peeling method, it was found that the adhesion force was several times that of that before the treatment after a treatment time of 300 seconds. An increase was seen.

A specific example of adhesion optimization is shown above.
The gist of the present invention is that by combining a fluorocarbon undercoat layer and plasma treatment, an undercoat layer can be produced with good controllability and a high degree of freedom using a simple device, and the recording layer and processing conditions are not necessarily limited. It goes without saying that the invention is not limited to the following examples.

(Example) PTFE (polytetrafluoroethylene) was sputtered using an Ar gas pressure of 1×10 ^-2 Torr and a discharge power of 200 W, and a film thickness of approximately 200
A thin film layer of 1.5 Å was formed. Then, Ar gas pressure 5×
Plasma treatment was performed for 30 seconds at 10 ^-3 Torr and discharge power of 50W.

Reactive sputtering of Te is performed on the treated undercoat layer, untreated undercoat layer, and substrate without undercoat layer in a mixed gas of SeF ₆ and Ar gas.
A thin film of about 400 Å thick containing Se and Se was formed and used as a recording layer.

The recording and reproducing characteristics of the above three types of optical recording media were evaluated under the following conditions. The disc-shaped substrate was rotated at 1800 rpm, and recording and reproduction were performed using GaAs semiconductor laser light with a wavelength of 830 nm on a track with a radius of approximately 30 mm from the rotation axis. The record is
Figure 3 shows the C/N ratio (Carrier to noise ratio) obtained using pulsed light at 3.63MHz and a duty of 30%.
shows the recording power dependence of In the figure, a is an untreated undercoat layer, b is a treated undercoat layer, and c is a case without an undercoat layer. While b has improved sensitivity compared to c, the C/N increases by 1 to 2 dB compared to a, and C/N is less dependent on recording power. As a result of SEM observation, it was found that in a, the pit length increases rapidly as the recording power increases, whereas in b, there is little change in the pit length.

Furthermore, in case b, the residue in the pit was smaller than in case c, and a uniform rim was formed.

Plasma processing conditions that provide a recording medium having a Te-SeF ₆ recording layer and having the characteristics shown in b can be determined by the ESCA method. That is,
It is desirable to determine the treatment conditions and treatment time so that the average atomic ratio of fluorine to carbon in a layer within 10 nm from the surface after treatment is 1.0 to 1.2 fluorine to 1 carbon. As shown in FIG. 4, the layer within about 10 nm from the surface of the untreated fluorocarbon sputtered film has a nearly uniform composition in the depth direction, whereas the treated film has a nearly uniform composition on the surface. It was also confirmed by the ESCA method that the ratio of fluorine atoms tends to increase the further into the film. Therefore, the average atomic ratio on the surface of the film to be treated is approximately 10 nm, which can be measured by the ESCA method.
The atomic ratio of all fluorine atoms to carbon atoms at a depth within

The reason why the pit length can be shortened while maintaining high sensitivity when the plasma-treated fluorocarbon undercoat layer of the present invention is used is thought to be due to the F/C depth distribution as described above. .

(Effects of the Invention) According to the present invention, not only the recording sensitivity can be improved, but also the pit shape and the shortest pit length can be improved in a well-balanced manner. Thereby, a high-speed, high-quality, high-density optical recording medium can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a longitudinal section of an example of the optical recording medium of the present invention, FIG. 2 is a schematic diagram of an apparatus used for manufacturing the optical recording medium of the present invention, and FIG. is the C/ of the recording medium obtained in the example.
FIG. 4 is a diagram showing the dependence of the N ratio on recording power, and FIG. 4 is a diagram showing changes in the ratio of fluorine atoms to carbon atoms on the surface of a fluorocarbon sputtered film. In the figure, 1 is a substrate, 2 is an undercoat film, and 3 is a recording layer.

Claims (1)

[Scope of Claims] 1. An optical recording medium in which an undercoat layer made of a fluorocarbon film is provided on a substrate and a perforated recording layer is disposed on the undercoat layer, in which the surface of the fluorocarbon undercoat layer is made free of defects. An optical recording medium characterized by being subjected to active gas plasma treatment. 2. The optical recording medium according to claim 1, wherein the fluorocarbon undercoat layer is a sputtered film of polyfluorocarbon. 3. The optical recording medium according to claim 1, wherein the inert gas that generates discharge when plasma-treating the surface of the fluorocarbon undercoat layer contains at least Ar. 4. The optical recording medium according to claim 1, wherein the perforation type recording layer is a thin film containing Te. 5. The drilling type recording layer is a deposited film containing Te and Se, formed by reactive sputtering in a mixed gas of selenium fluoride gas and Ar gas, using a metal containing Te as a target material, and A patent claim characterized in that the average atomic ratio of fluorine to carbon within 10 nm from the surface of the fluorocarbon layer in contact with the recording layer after plasma treatment is 1.0 to 1.2 fluorine to 1 carbon. The optical recording medium according to item 1.