JPH02223479A - Optical recording medium - Google Patents

Abstract

PURPOSE:To form stable pits to enhance a recording sensitivity by a method wherein an optical recording medium is formed by providing a recording film made of an alloy film mainly composed of Te and an oxide film mainly composed of Te with a specific thickness successively on a substrate. CONSTITUTION:On a substrate 1 made of polycarbonate or the like, a Teflon film 2 is provided. On the film 2, an alloy film 3 mainly composed of Te is formed as a recording film. Furthermore, the surface of the alloy film 3 is forcibly oxidized to form an oxide film 4 thereon. As the alloy film 3, for example, a Te-Se-Pb alloy is used. The oxide film 4 is formed by oxidizing Te in the alloy film 3 to TeO2. The film thickness of the oxide film 4 is 10 - 25Angstrom . The obtained optical recording medium maintains mechanical and chemical stabilities and allows a writing laser power to effectively act to form pits ; thus, a recording sensitivity and a writing speed can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical recording medium whose recording film is a metal thin film layer containing Te as a main component.

[Prior Art] Conventionally, in optical recording media in which information is recorded by irradiating laser beams to form thank-you pits, Te is used as the recording film because Te has a low melting point. A metal thin film layer mainly composed of is often used. When this metal thin film layer is heated to a temperature above its melting point by irradiation with a laser beam, that portion melts and is drawn to surrounding unmelted portions by surface tension, forming holes, that is, pits 1-.

An optical recording medium using a recording film made of such a material is one in which the surface of the recording film is forcibly oxidized and a Te oxide film with a thickness of 50 nm is provided on the surface of a metal thin film layer mainly composed of Te. It is known (Japanese Unexamined Patent Publication No. 6120932). According to this technology, the Te oxide film is mechanically strong and
While Te is easily oxidized even in the air, when the surface of a Te film is covered with a forcibly oxidized Te film, this film is chemically stable and can cause oxidation of the internal Te film and even Erosion by chemicals and the like is prevented, and a mechanically and chemically stable optical recording medium can be obtained.

In addition, since the recording film containing Te as a main component is a metal (alloy), its thermal conductivity is high, and when the recording film is directly irradiated with a laser beam, the heat generated by this will quickly travel through the recording film. The heat is scattered, and the heat cannot be used effectively.
High laser power is required to form pits. However, in the prior art described above, the Te oxide film acts to accumulate heat from the irradiated laser beam, and this accumulated heat causes pits to be formed in the recording film, resulting in improved sensitivity.

[Problems to be Solved by the Invention] In recent years, it has become increasingly desirable to increase the recording speed of information on optical recording media, and for this purpose, it is necessary to further increase the recording sensitivity and increase the writing speed. There is a need to.

However, with the above optical recording media, there is a limit to the recording sensitivity, and in order to shorten the recording time to meet the requirements, it is necessary to increase the laser power. However, there was a problem in that stable pit formation could not be achieved.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording medium that solves these problems and can significantly increase recording sensitivity while maintaining stable pit formation.

[Means for solving the problem] The oxide film mainly composed of TeO2 on the alloy film mainly composed of Te has poor thermal conductivity, so it does not dissipate the heat generated by laser beam irradiation to the surroundings. It acts to accumulate.

However, if this oxide film is too thin, the amount of heat stored in the oxide film is small, and most of the supplied heat is quickly dispersed to the surroundings. In other words, the recording film has high thermal conductivity similar to an alloy film containing Te as a main component, and cannot utilize heat effectively.

For this reason, high laser power is required to form the pins 1 to 1. Also, if the oxide film is too thick, a very large amount of heat will accumulate in the oxide film, which will cause unreasonably sized pits to form in the alloy film. In order to prevent this, the laser power may be lowered, but the amount of heat reaching the alloy film decreases, resulting in a decrease in recording sensitivity. For this reason, it is very difficult to set a laser power that satisfies good pit formation and improved recording sensitivity at the same time, and consideration must also be given to fluctuations in laser power, and in reality, it is not possible to satisfy both at the same time. %N0 - In order to achieve the above object, the present invention takes the above points into consideration and optimally sets the film thickness of the oxide film.
~25 people.

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

FIG. 1 is a sectional view showing an embodiment of an optical recording medium according to the present invention, in which l is a substrate, 2 is a Teflon film, 3 is an alloy film,
4 is an oxide film.

In the figure, a Teflon film 2 is provided on a polycarbonate substrate 1, and an alloy film 3 containing Te as a main component is provided thereon as a recording film. Then, on the surface of this alloy film 3, an oxide film 4 is provided by forcibly oxidizing the alloy film 3.

For example, a Te-8e-Pb alloy is used as the alloy film 3, and the oxide film 4 is made by oxidizing Te in the alloy film 3 to TeO2. The thickness of the oxide film 4 is 10 to 25.

Next, this example will be explained in detail, and a measurement example will be shown in which the performance was compared with that of a comparative example.

Example 1: A Teflon film with a thickness of 500 A was formed by sputtering Teflon on a 5.25 inch φ polycarbonate 1 substrate using an RF magnetron sputtering device.
Then, on top of that, TeTe-8e (10%)-Pb
(5wt%) of the alloy was sputtered to form an alloy film with a thickness of 300 mm. The thus prepared disk was heat treated at 90° C. in air for 1 hour to grow an oxide film on the surface of the alloy film. Thereafter, the two disks thus obtained were bonded together with the recording surface facing inside.

Example 2: A disk was produced in the same manner as in Example 1 above, but the heat treatment conditions were 80° C. in a 50% oxygen enriched atmosphere.

It was set as 1 hour.

Comparative examples are as follows.

Comparative Example 1: A disk was produced in the same manner as in Example 1 above, but the heat treatment was omitted.

Comparative Example 2: A disk prepared in the same manner as in Example 1 was heated to 20″C.
1. It was left in an atmosphere for one month.

Comparative Example 3: A disk prepared in the same manner as in Example 1 was heat treated, but the heat treatment conditions were air atmosphere at OO° C. for 2 hours.

Examples 1 and 2 and Comparative Example 1 obtained as above
The film thickness of the oxide film in ~3 was measured by X-ray photoelectron spectroscopy (xps
) Determined by analytical method. In this method, the sample is irradiated with X-rays and the film thickness is measured from the intensity of the photoelectron signal emitted from the sample. Here, the photoelectron signal due to metal Te in the alloy film is measured. The thickness of the oxide film was determined from the ratio of the peak height to the peak height of the photoelectron signal measured by the oxide Te in the oxide film. Here, if this ratio is R, and R=peak height of metal Te/peak height of oxide Te, then the film thickness a of the oxide film is expressed as follows.

However, λ is the mean free path of photoelectrons.

An Mgkα ray source was used as the X-ray source, and the output was 20 mA.

It was driven at 12kV. When excited by this, the metal T
e and electrons in the 3 d R/2 orbit of Te in the oxide Te are detected as photoelectrons. The mean free path λ of this electron is 13.

The results of measuring the peak height ratio and the film thickness of the oxide film of Examples 1 and 2 and Comparative Examples 1 to 3 using this method are shown in the following table.

<Table> As is clear from this table, in Examples 1 and 2, the thickness of the oxide film was within the range of 10 to 25 layers.

Next, for Examples 1 and 2 and Comparative Examples 1 to 3, writing was performed with various laser powers, and this was read to determine the modulation rate (=reflectance of non-pit areas/reflectance of pit areas). Measurements were made. The results are shown in FIGS. 2 and 3. However, the writing condition at this time is that the number of revolutions of the disk is 1.
80Orpm f = 24-00 rpm, laser beam diaphragm lens numerical aperture (NA) = 0.53,
FIG. 2 shows the modulation rate when the rotation speed is 1800 rpm, and FIG. 3 shows the modulation rate when the rotation speed is 2400 rpm. In any case, in Examples 1 and 2, a higher modulation rate can be obtained with lower laser power than in Comparative Examples 1 to 3.

Therefore, Examples 1 and 2 have higher recording sensitivity than Comparative Examples 1 to 3, and can increase the writing speed with low laser power. Furthermore, since it is possible to perform writing with a high modulation rate with low laser power, it is possible to make the formed pits small in diameter for good reading, and to achieve high recording density by reducing the track pitch.

Figure 4 shows the change in modulation rate with respect to the film thickness of the oxide film when the writing laser power was kept constant at 6 mW from the measurement results shown in Figure 2, and the horizontal axis shows the metal Te peak determined by XPS analysis. The ratio R of the height to the oxide Te peak height and the film thickness a of the oxide film are taken, and the modulation factors on each side in FIG. 2 are connected by a curved line.

As is clear from the figure, the modulation rate decreases if the oxide film is made too thin or too thick. The minimum required modulation rate is 70%, and in the case of Figure 4, in order to ensure a modulation rate of 70% or more, the ratio R between the metal Te peak height and the oxide Te peak height must be 0.25 to 1. Therefore, the film thickness a of the oxide film is set in the range of 20.9 to 7.4.
It needs to be set within the range of people.

By the way, if an oxide film with a thickness thinner than 10% is formed by forced oxidation through heat treatment, the mechanical and chemical stability of the disc will not be achieved, and the disc will be easily scratched and susceptible to chemicals. There's a problem. Furthermore, as is clear from a comparison between FIG. 2 and FIG. 3, when the rotational speed of the disk is lowered, the modulation rate increases for a constant laser power, regardless of the thickness of the oxide film. Therefore, even if the oxide film is thick, a high modulation rate can be obtained by lowering the rotational speed of the disk, thereby making it possible to narrow the pit interval and increase the recording density. However, there is a limit to this pit spacing, and therefore there is a limit to increasing the thickness of the oxide film that can achieve a high modulation rate. Therefore, in the present invention, the maximum value of the oxide film is set to the above value (2
The number of participants will be 25, which is slightly larger than the number of participants (0.9 people).

[Effects of the Invention] As explained above, according to the present invention, the writing laser power can be effectively applied to pit formation while maintaining mechanical and chemical stability, thereby greatly increasing the recording sensitivity. ,
An excellent effect can be obtained in that the writing speed can be significantly shortened.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of an optical recording medium according to the present invention, and FIGS. 2 and 3 show a comparison between the relationship between the writing laser power and the modulation rate in proportion to the embodiment according to the present invention. FIG. 4 is a graph showing an example of measurement of the relationship between the thickness of the oxide film and the modulation rate. 1...Substrate, 3...Alloy film, 4...Oxide film. (0n) ↓Norishimi&

Claims (1)

[Claims] An optical recording medium in which an alloy film containing Te as a main component is used as a recording film, and an oxide film containing Te as a main component is provided on the surface of the alloy film, characterized in that the thickness of the oxide film is 10 to 25 Å. optical recording medium.