JPS62298944A - Optical recording medium - Google Patents

Abstract

PURPOSE:To permit not only the improvement of recording sensitivity but also the improvement balanced well in pit shape and shortest pit length and to provide the higher speed, quality and density by subjecting the surface of a fluorocarbon under coat layer to an inert gas plasma treatment. CONSTITUTION:The thin fluorocarbon film is deposited to 20-1,000Angstrom , more preferably 50-300Angstrom on a substrate 1 by a plasma polymn., sputtering or vapor deposition method; thereafter, the surface of the fluorocarbon film is subjected to the inert gas plasma treatment to form the under coat layer 2 and to optimize the adhesive power of various recording layers to the underlying layer. The pit length can be shortened while the high sensitivity is retained when the fluorocarbon under coat layer subjected to the plasma treatment is used.

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) Conventionally, a thin film of metal such as Te or Ei is used as an optical recording medium in which holes (pits) are formed by irradiating a thin film formed on a substrate with a laser beam. It is known.

Furthermore, in order to increase the stability over time, the use of Te-based alloy thin films made of Te, Se, etc., and plasma polymerized films containing these metals are 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 in these recording media include plastic, glass, metal, and substrates coated with photocurable resin.

It is necessary that the recording layer material melted by the single 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. 9024LA). The factors that determine the adhesion force are the surface tension of the substrate surface and the recording layer material, the molecular weight of the substrate surface layer, the degree of crosslinking, etc., but if the adhesion force is small, the bit hole can be drilled in a short time with a lower laser beam power. can be formed. 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 from the surface of the undercoat layer in contact with the recording layer, /On
An optical recording medium has been found in which the atomic ratio of carbon to fluorine in a layer in m is 1 or more as measured by the EEIIOA method (soft X-ray excitation photoelectron spectroscopy): fluorine to carbon/. (Patent Application Sho-Otsu 0-29♂/ri7) (Problems to be Solved by the Invention) On the other hand, in addition to the above-mentioned characteristics, recording media have a large storage capacity, that is, high density. It is required to be able to record. 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, high-speed recording using a disk-shaped disk requires a drive system that performs recording and reproduction to shorten the duration of irradiation with laser light for drilling to <Lf.
C, the pulse repetition frequency is increased and the spot size of the focused laser beam is reduced, and
This is achieved by rotating the disk at high speed.

When 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 a recording layer and an undercoat layer, It is determined by the spot size of the laser beam focused on the recording medium surface, the laser beam irradiation time, the laser beam intensity, the relative movement speed of the recording medium surface with respect to the laser beam, etc. For optical systems generally used for optical recording and the wavelength of semiconductor laser light around ♂00 nm, the laser light spot size is limited to a diameter of about 7 μm, and the shortest pit length is at least the same size as this spot size. becomes. If the thermal conductivity of the recording medium is high and the area melted by laser beam irradiation is large, or if the adhesion between the recording layer and the undercoat layer is too weak and a large amount of material is removed, formation of The shortest possible pit length tends to be large. Furthermore, in the above two media, 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 the disk is rotated at high speed, when recording with a short pulse length laser beam, the unit area on the medium surface is Since the energy density of the irradiated laser light becomes smaller, the power of the laser light required for drilling becomes greater, and the demand for higher sensitivity of the medium becomes even more severe.

Therefore, in order to meet the above requirements, the combination of the recording layer and its underlayer (substrate or underlayer) is an extremely important element. In other words, in order to shorten the shortest pit length,
For example, to improve sensitivity by using a dye such as trocellulose, guanine, or phthalotaanine as an undercoat layer on an organic substance that has a high adhesive force but decomposes and sublimates at low temperatures. How to do it (Proceedings of the 32nd Applied Physics Association Conference (/ri♂!, Spring)
p//j), 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 was formed on a film of a copolymer of fluorocarbon and hydrocarbon and the recording sensitivity was measured, increasing the ratio of fluorocarbon in the copolymer ), it is possible to reduce the adhesion force and improve recording sensitivity (D, J.

Broer ana L, Vriens appl p
hys Al1 p107(/ri1?)) On the contrary, by plasma-treating the entire surface of polytetrafluoroethylene resin, the present inventors have developed such a fluorocarbon film. Focusing on the good controllability of the adhesion force in the fluorocarbon thin film, we conducted various studies on undercoat layers made of thin fluorocarbon films.We found that a fluorocarbon undercoat that improves adhesion and shortens the minimum bit length while improving sensitivity and pit shape. An optical recording medium having a film was obtained and the present invention was achieved.

That is, the gist of the present invention resides in light in which an undercoat layer made of a fluorocarbon film is provided on a substrate, and a perforation type recording layer is disposed on the undercoat layer.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing seven examples of specific structures of the optical recording medium of the present invention, in which (1) is a substrate, and (2) is a fluorocarbon undercoat film disposed on the substrate (1). , (3) is the membrane (2
) and (4) are grooves for track servo.

Examples of the substrate (1) of the recording medium according to the present invention include plastics such as acrylic resin and polycarbonate resin, glass, or aluminum coated with an ultraviolet curing resin.

In the present invention, a fluorocarbon thin film of 20 to 10 ool is preferably formed on this substrate by plasma polymerization, sputtering, or vapor deposition. After depositing 0~300λ, the surface of the fluorocarbon film is treated with inert gas plasma to form an undercoat layer (2), and various recording layers (
For 3), optimize the adhesion to the base.

A fluorocarbon plasma polymerized film or polyfluorocarbon sputtering, at, e, on the substrate (1).
Perfluoroalkenes such as veF2, perfluorohexane, perfluorobenzene, etc., are gases at room temperature,
Alternatively, even if the fluorocarbon is a liquid, it has a sufficiently high vapor pressure to allow glow discharge by filling a vacuum container with the fluorocarbon vapor at 10-'' Torr or more, and preferably has a high degree of fluorine substitution.These fluorocarbons (by using capacitive or inductive discharge as a monomer) to form a plasma polymerized film.Polyfluorocarbons include polytetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and tetrafluoroethylene rubber. Using fluoroalkoxyethylene copolymer resin etc., Ar
A sputtered film is formed by sputtering with an inert gas such as, or a mixed gas of an inert gas and the monomer.

For the recording layer (3), a Te-based alloy is usually used, especially a Te-based alloy.
-8e alloy is good. To form a Te-S e type recording layer, use Te or an alloy containing Te as a main component as a target, introduce selenium fluoride gas into the sputtering equipment, and form a sputtering layer. Good. What is the content of Se in the recording layer? It is preferable to set the amount to about 2 to 2 atomic percent.

FIG. 2 shows an example of an apparatus for forming a recording layer by sputtering after a sputtered film or a plasma polymerized film of polyfluorocarbon is prepared and subjected to plasma treatment. 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. When the recording layer is an alloy containing Te, the plasma treatment is performed so that the average atomic ratio of fluorine to carbon in the layer within /Onm from the surface of the fluorocarbon layer in contact with the recording layer changes from 〇 to fluorine to carbon/. It is better to process it so that it is about λ.

In Fig. 2, (2), (3), and (4) are electrodes for applying high frequency waves), and they basically have the same structure.
4) is made of the material to be sputtered (5)
is the holder with the board (6) set, 11II
, one chamber can be transported in this order. (7), (8),
(9) is a gas inlet for generating electric discharge), and through (7) and (9) in the film forming chamber, I, l[,
Arma North introduces a mixed gas of reactive gas and Ar gas. For example, Ar gas is introduced into the plasma processing chamber through (8). Here, 1. Differential exhaust chambers α■ and αη are provided between chambers II and II to independently control the gas level and pressure in each chamber. Also, (2) is the exhaust port, α→
is the RF power source. In the first chamber, if the material of the electrode (2) is changed to a material that is difficult to be sputtered by plasma as in (3) and fluorocarbon monomer gas is introduced from the inlet (7), a plasma polymerized film can be produced. can.

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 a film is formed on the substrate (6) in the first chamber. The surface of the fluorocarbon film may be exposed to the plasma.

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, in particular the discharge power and the treatment time exposed to the plasma, and the spacing between the substrate (6) and the electrode (3), so that the recording layer and the undercoat are The adhesion force with the layer can be controlled over a wide range and optimized for various recording layers.
When the surface tension of the fluorocarbon film is high, the density and molecular structure of the surface crosslinked layer increase due to 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. -4f, PT
A sputtered film of FE (polytetrafluoroethylene) was prepared, and then Ar gas pressure was applied to
Ar plasma treatment was performed at a discharge power of ioow, and the contact angle with water and the change in the atomic ratio of fluorine atoms to carbon atoms (Flo) of the layer within /Onm from the surface measured by the ESOA method were measured. In addition, ESOA
The method of measurement according to the method is as described in Japanese Patent Application No. 1987-29/7.

It was confirmed that the contact angle and Flo decreased as the treatment time increased. On the other hand, a 're-8eF6 recording layer (disclosed in Japanese Patent Application No. 1986-/7.26≠7) was formed on the plasma-treated fluorocarbon undercoat layer, and attached by a simple peeling method. When the adhesion strength was measured, it was found that after a treatment time of 300 seconds, it increased several times compared to before treatment.

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.)
It goes without saying that the recording layer and processing conditions are not necessarily limited to the following examples.

(Example) PTFE (polytetrafluoroethylene) was spun with Ar gas pressure/X 10-” Torr and discharge power of 200 W, and a film thickness of approximately A thin film layer of 200 people was formed.Subsequently, Ar gas pressure jX#)-3T
orr, discharge power! Plasma treatment was performed for 130 seconds under OW.

On the above-mentioned undercoat layer to be treated, the untreated undercoat layer, and the substrate without undercoat and Pig, a reactive sputtering process of Te is performed in a mixed gas of SeF and Ar gas to form a film containing Te and Se. A thin film of about 200 layers was formed and used as a recording layer.

Do not evaluate the recording and reproducing characteristics of the above three types of optical recording media under the following conditions.

The disk-shaped substrate was rotated at /IOOrpm, and the wavelength was 30tm from the axis of rotation. 30mm
Recording and reproduction were performed using a GaA15 semiconductor laser beam.

The record is 3. Figure 3 shows the C/N ratio (Oarriey
(to noise) atlo). In the figure, (c)] is an untreated undercoat layer, (6) is a treated undercoat layer, and (c) is a case without an undercoat layer.

While (b) and (c) yo) also have improved sensitivity, (a)
In addition, the O/N increases by 2 dE, and the dependence of the C/N ratio on the recording power is reduced. This is the result of SF, M observation (
It was found that this is because in (a) the bit length increases rapidly as the recording power is increased, whereas in ('b) there is little change in the bit length.

Furthermore, in (b), the residue in the bit was smaller than in (C), and a uniform rim was formed.

Plasma processing conditions for obtaining a recording medium having a T6-8eF type recording layer and having the characteristics as shown in (6) can be determined by the ESCiA 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 the layer within / Onm from the surface after treatment is from 0 to 2 for fluorine to carbon /. . Here, as shown in Fig. ESC! is that the ratio of fluorine atoms tends to increase from the surface to the inside of the film. Confirmed by method A. Therefore, the average atomic ratio on the surface of the film to be processed is the atomic ratio of total fluorine atoms to carbon atoms at a depth of about /Onm that can be measured by the ESOA method.

The reason why the bit 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 bit length can be improved in a well-balanced manner. As a result, a high-speed, high-quality, and high-density optical recording medium can be obtained. 1

[Brief explanation of the drawing]

1@ is a drawing schematically showing a longitudinal section of an example of the optical recording medium of the present invention, FIG. 1 is a schematic diagram of an apparatus used for manufacturing the optical recording medium of the present invention, and FIG. 3 1 is a drawing showing the recording power dependence of the C/N ratio of the recording medium obtained in the example, and FIG. In the figure, / indicates the substrate 1.2I'i undercoat film, and 3 indicates the recording layer, respectively.

Claims (5)

[Claims] (1) In 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 arranged on the undercoat layer, the surface of the fluorocarbon undercoat layer is treated with inert gas plasma. An optical recording medium characterized by: (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 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 for fluorine to 1 carbon. An optical recording medium according to claim 1.