JPS6374139A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the quality and density of recording by specifying the atom ratio of carbon and fluorine on the surface, in contact with a recording layer, of an under coating layer consisting of a fluorocarbon film. CONSTITUTION:The thin film consisting of the polyfluorocarbon is deposited by a plasma polymn. method on a substrate 1 formed by coating a UV curing resin on plastic, glass or aluminum, etc., to form the under coating film 2. The recoding layer 3 consisting of Te-SeF6 type is formed on the film 2 and grooves 4 for a track servo are provided thereon. Good characteristics are obtd. and the quality and density are improved by controlling a gaseous monomer of tetrafluoroethylene or hexafluoropropylene which is the raw material and other conditions in such a manner that the atom ratio of the fluorine atoms and carbon atoms on the film 2 surface attains >=0.8-<1.4 fluorine to 1 carbon in the value measured by an ESCA method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium capable of high-density and 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 substrate is evaporated or melted away by heat generated by irradiating the thin film with a laser beam.

(Prior Art) Metal thin films such as To and Bi have traditionally been used as optical recording media in which holes (bits) are formed by irradiating a thin film formed on a substrate with a laser beam. There is. Furthermore, in order to increase stability over time, Te-based alloy thin films made of Te, Se, etc., and plasma polymerized films containing these metals are used. 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, the substrates used for these recording media include plastic, glass, metal, etc., and those on which a photocurable resin film or the like is formed are exemplified.

In order to perforate a thin film using a laser beam in a system consisting of the above-mentioned substrate and a thin film recording medium, it is necessary that the film material melted in the bath by laser heating be separated by the adhesion force with the substrate. For such purposes, it has been considered to provide an undercoat layer made of a thin fluorocarbon film between the recording layer and the substrate (see Japanese Patent Publication No. 9-902'll).
, issue). Factors that determine the adhesion between the substrate and the film material include the surface tension of the substrate surface in contact with the recording layer and the material forming the recording layer during melting, the molecular weight of the substrate surface layer, the degree of crosslinking, and the like. The relationship between the recording layer and the substrate is that the adhesion force between the two is small.

Bits can be formed in a short time with lower laser source power. This means improved recording sensitivity, which enables high-speed file recording and the use of inexpensive low-power semiconductor lasers.

However, in order to perform higher quality recording, it is required not only to improve the sensitivity, but also that the formed bit shape have a clear outline and be -m.

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 a 10 nm layer from the surface of the undercoat layer in contact with the recording layer.
The atomic ratio of carbon and fluorine in the layers within FXscA (soft
We proposed an optical recording medium in which the measured value by linear excitation photoelectron spectroscopy is 9 or more compared to carbon/fluorine/. (Patent Application Otsu 0-29g/97) (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 recording is possible. things are required. In order to improve the storage capacity of punch-type optical recording media, it is required to make the bit size as small as possible. Because the thermal conductivity of the recording medium is high, the area that is removed by bath melting by laser beam irradiation may become thick (or the adhesive force between the recording layer and the undercoat may be too weak and the material may be removed). If the number of children increases.

The bit size tends to increase, making high-density recording impossible. In addition, with the above-mentioned media, the bit size tends to fluctuate sensitively even with slight fluctuations in the laser source power.

It becomes difficult to record stable and accurate digital signals.

Furthermore, in addition to the above-mentioned problems regarding the bit shape, when recording with a short pulse length laser beam or rotating a disk at high speed, especially at the outer periphery of the disk, the number of units per unit area on the medium surface Since the energy density of the laser light irradiated over time becomes smaller, the laser light output required for drilling becomes larger, and the demand for higher sensitivity of the medium becomes 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. In other words, shorten the shortest pit length (in order to
It is desirable that the adhesion force be large, but on the other hand, in order to achieve high sensitivity, it is desirable that the adhesion force be small.

(Means for Solving the Problems) The present inventors have discovered that by controlling the composition ratio and structure of carbon and fluorine in the fluorocarbon thin film, the bonding layer between the undercoat layer made of the fluorocarbon thin film and various recording layers can be We have arrived at the present invention to obtain an optical recording medium that provides high sensitivity and improved pit shape while controlling the adhesion force and thereby reducing the minimum bit size.

That is, the gist of the present invention is to provide an optical recording medium in which an undercoat layer made of a fluorocarbon film is provided on a substrate and a perforation type recording layer containing Te is disposed on the undercoat layer. 10n from the surface in contact with the recording layer
The optical recording medium is characterized in that the atomic ratio of carbon to fluorine in a layer within m, as measured by the ESOA method, is at least o, g and less than heg of fluorine per l of carbon.

5 ESOA method is an abbreviation for soft X-ray excited element electron fractionation method, which uses the energy spectrum of photoelectrons ejected from atoms in a sample compound by irradiation with soft X-rays to determine the area near the surface of the sample. This is a method of analyzing the types of elements and chemical bonding states of . In this method, since the above-mentioned photoelectron transmission ability is small, the thin film can be analyzed from the surface at 10T.
Fluorine IB orbit (F+
s) spectrum and carbon 15 (C!, B) orbital spectrum were measured. The Fl[3 spectrum consists of a single peak with a binding energy centered around A g t eV, and the CI8 spectrum consists of multiple peaks with binding energies centered around 1.2 to Cock ev. Ru. The atomic ratio of carbon atoms and fluorine atoms is F above.
It is derived from the ratio of the integrated intensity of the 1s peak and the integrated intensity of the C1S spectrum.

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 a recording medium according to the present invention, and (1) is a substrate.

(2) is a fluorocarbon subbing film disposed on substrate (1), (3) is a recording layer formed on film (2), and (4)
is the groove for the 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 film made of fluorocarbon is provided on this substrate. Specifically, for example, a polyfluorocarbon thin film is formed at 20 to 10 OOA by plasma polymerization method.
, preferably 50 to 300^, to form an undercoat layer (2) and optimize adhesion to the undercoat for each recording layer (3).

Used for plasma polymerization (7mers of fluorocarbons include tetrafluoroethylene, hexafluoropropylene nato bar 70 alkene, and hahalffluorochlorone chlorohexane,
Bar 70 benzene, etc., which is a gas at room temperature, has a sufficient vapor pressure even if it is liquid, and the vapor of the fluorocarbon is placed in a vacuum container at 0-3 TOrr or more; however, glow discharge is possible. It is acceptable as long as it has a high degree of fluorine substitution. In particular, ethylene tetrafluoride and propylene hexafluoride are molecules with high vapor pressure, high polymerization rate, low cost, and easy handling. A plasma polymerized film can be formed by using a chemical or inductive discharge at °C.Another method for forming a fluorocarbon film is to form a polyfluorocarbon such as poly/tetrafluoroethylene by sputtering or the like. be.

FIG. 2 shows an example of an apparatus for forming a recording layer by sputtering after producing a fluorocarbon plasma polymerized film.

In the figure, (5) is a vacuum container, the interior of which is divided into Ω chambers. Perform plasma polymerization in the first chamber, and then
A recording layer is formed in a chamber. In Figure 2, (6),
(7) is an electrode for applying high frequency.

Although they basically have the same structure, (7) is a target made of a material to be sputtered, whereas (6) is a target made of a material 5 (stainless steel) that is difficult to sputter.

Ta, etc.) are used. (8) is a holder in which the substrate (9) is set, and can be transported in the order of chambers (1) and (2). C1 and α◇ are gas inlet ports for generating discharge, fluorocarbon monomer gas is introduced from αO, and Ar or a mixed gas of Ar and a reactive gas such as selenium fluoride gas is introduced from αυ. Here, 1. (2) Between the chambers are provided α differential exhaust chambers for independently controlling the type and pressure of gas in each chamber. Further, C11 is an exhaust port, and α→ is an RF power source.

The composition ratio (atomic number ratio) of fluorine atoms and carbon atoms on the surface of the fluorocarbon film obtained in the capacitively coupled plasma polymerization apparatus as described above, Flo is the monomer gas used as the raw material, and the shape of the apparatus.

Although it depends on the discharge conditions, especially the discharge power and the monomer gas pressure, values in the range of about 0.2 to S/S can be easily obtained. On the other hand, in sputtering polyfluorocarbon films, due to limitations on the heat resistance of polyfluorocarbon resins that can be used as targets,
As for i, only about 1.7 can be obtained from i. F
The smaller lo is, the less fluorine atoms there are (the degree of cross-linking between carbon atoms is high, and the film structure is high).

There is a tendency for the adhesion force with the recording layer to increase.

From the point of view of controlling adhesion force, plasma polymerized membranes have a wider range and can be controlled. The present inventors applied an undercoat layer made of the plasma-polymerized fluorocarbon film to a perforation-type recording layer made of a metal thin film containing various types of Te, and achieved a balance between sensitivity, bit shape, and minimum bit size. In order to achieve this improvement, we optimized the adhesion between the recording layer and the undercoat layer. As a result.

The atomic ratio of carbon to fluorine in the layer within 1 Onm from the surface of the undercoat layer in contact with the recording layer is 0, g or more of fluorine per carbon 1, less than 9, preferably 0.9 or more/, 3 A recording medium with the best characteristics was obtained when the following conditions were used. When Flo is smaller than o, g, the effect of improving sensitivity is smaller than when the recording layer is directly formed on polycarbonate resin etc. (If Flo is larger than /, !I, the bit size is Thick (it tends to become thick).

(Example) (Example/) A monomer gas of propylene hexafluoride was introduced into a vacuum container, and the pressure was set to /X/0-2 TOrr. Diameter 3
Between an inch stainless steel circular cathode and an anode of about the same size and equipped with a disc-shaped polycarbonate resin substrate, there is a /,? , j AMH2 high frequency voltage is applied.

This produced a glow discharge. The discharge power was SOW, and the distance between the parallel plate electrodes was 100 mN. A plasma polymerized film with a thickness of about 200 mm was obtained under the above conditions and used as an undercoat layer. The fluorine to carbon atomic ratio F/C of the hexafluoropropylene plasma polymerized film is 7.2 fluorine to carbon/carbon.
Met.

On the above-mentioned undercoat layer, as a recording layer, Te is mixed with Ar and SeF.
6 Film thickness obtained by sputtering in a mixed gas of about 1 Ioo^
Te-3eF6 type media (patent application 1.0-291s!; 2
A film similar to that disclosed in No. 0) was formed. For comparison, a sputtered film of polytetrafluoroethylene (film thickness approximately λθθ^) with Flo of /, 5 was used as an undercoat layer.

Similarly, for the case without undercoat layer, Te-8eF
, a system recording layer was formed.

The recording and reproducing characteristics of the above three types of optical recording media were evaluated under the following conditions. The disc-shaped substrate is / g
Rotate at 00 rpm and have a radius of approximately JOm from the rotation axis.
, a GaAs semiconductor with wavelength g 30 nm v ! - Recorded - Played back. The record is J, A
,? The test was carried out using a pulse source of MHz and a duty of 30%.

Figure 3 shows the C/N ratio (Carrier to noise).
The dependence of ratio) on recording power is shown. In the figure (a
) is Flo = /, S When a polytetrafluoroethylene sputtered film is used as an undercoat layer, (b) is Flo
== /, When the hexafluoride propylene plasma polymerized film of 2 is used as an undercoat layer, (C) is the case without an undercoat layer. (B) has improved sensitivity compared to (C), but O/N increases by 2 to 3 dB compared to (a).

The dependence of the C ratio on the recording power is small. this is.

As a result of SEM observation, it was found that in (a), as the recording power was increased, the bit size increased rapidly, whereas in (), the bit size did not fluctuate much. In , ■, there was less residue in the bit than in (C), and a uniform rim was formed.

(Example 2) A plasma polymerized film (F/C=/, /) with a film thickness of 200^ was formed in the same manner as in Example/, except that the monomer gas was changed to ethylene tetra7ide. This was used as an undercoat layer. In addition to the above tetrafluoroethylene plasma polymerized film, similarly to Example 1, a polytetrafluoroethylene sputtered film (F/C=/, , lr), three types of substrates without undercoat, and On the undercoat layer, nitrogen and A
Reactive sputtering of an alloy target of 70gg%, Sθ/, 2% (atomic ratio) in a mixed gas with r,
A thin film containing Te and Sθ with a thickness of qoθ^ (patent application AO-
/! ;/jtO! forming a film similar to that disclosed in;
It was used as a recording layer. Recording was performed on the above three types of optical recording media in the same manner as in Example.

The playback characteristics were evaluated.

When a polytetrafluoroethylene sputtered film is used as an undercoat layer, the sensitivity is extremely good, but the adhesion is too weak, resulting in irregular bit shapes and only large holes. For this reason, the C/N ratio is highly dependent on location and recording power, making it impossible to accurately record and reproduce digital signals.

When a plasma polymerized film of tetrafluoroethylene is used as an undercoat layer (and when there is no undercoat layer,
The properties shown in Figure 3) and (C) were similar, and the best properties were obtained with the plasma polymerized film undercoat layer.

(Effects of the Invention) The fluorocarbon film undercoat layer of the present invention not only improves the sensitivity of the recording medium (but also achieves a well-balanced improvement in the recording and reproducing characteristics, especially for high-density optical A digital recording medium can be realized.

[Brief explanation of the drawing]

FIG. 1 shows an example of the structure of a recording medium according to the present invention, FIG. 2 shows an example of a sputtering apparatus for forming a recording layer, and FIG. 3 shows an example of the structure of a recording medium according to the present invention. Media C7N
The recording dependence of the ratio is shown. In the figure, (1) two substrates, (2): undercoat film, (3)
:Record layer Akira 3 illustrations 8 pairs of notes 80 words

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 perforation type recording layer made of a thin film containing Te is disposed on the undercoat layer, the recording layer of the undercoat layer is An optical recording characterized in that the atomic ratio of carbon to fluorine in a layer within 10 nm from the surface in contact with the surface is 0.8 or more and less than 1.4 for 1 carbon to 1 fluorine, as measured by the ESCA method. Medium for use. (2) The optical recording medium according to claim 1, wherein the fluorocarbon film is a fluorocarbon plasma polymerized film. (3) The optical recording medium according to claim 1, wherein the fluorocarbon monomer gas is tetrafluoroethylene or hexafluoropropylene. (4) The perforation 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. An optical recording medium according to claim 1, characterized in that: (5) The above-mentioned hole-type recording layer is a deposited film containing Te and Se formed by reactive sputtering in a mixed gas of nitrogen gas and Ar gas using an alloy containing Te and Se as a target material. An optical recording medium according to claim 1, characterized in that: