JP4859793B2 - Manufacturing method of substrate for optical recording medium - Google Patents

Description

The present invention relates to a method for manufacturing a substrate for an optical recording medium.

Conventionally, a technique related to an optical disk applied to a high NA pickup has been studied.
For such an optical disk, a transfer substrate is obtained by injection molding using a stamper (mold) having a functional shape (fine irregularities) for forming a predetermined signal by photolithography, and then a magnetic recording layer or a phase change It can be produced by forming a recording layer and further forming a coating layer (protective layer, light transmission layer, etc.).

The covering layer constituting the protective layer and the light transmitting layer is generally formed by a spin coating method using a liquid curable resin, but this method makes it easy to make the film thickness in the circumferential direction uniform. However, there is a problem that it is difficult to make the film thickness in the radial direction strictly uniform.
For example, in a phase change type optical disk, when a light transmission layer is formed by spin coating a liquid resin on a dielectric layer (ZnS · SiO ₂ ), variation in film thickness results in an optical phase difference, resulting in interference fringes. It is known that the recording / reproducing characteristics deteriorate. Furthermore, since the outermost surface of the spin-coated liquid resin is in contact with air, even if it is in a clean room or a clean booth equipped with a HEAP filter, film defects can be caused by adhesion of a small number of particles. There is also a risk of being invited.

As described above, it has been a conventional technical problem to form a resin film having excellent film thickness uniformity in the radial direction and having no defects.
In this regard, for example, a technique has been proposed in which a center portion of an optical disk substrate is covered and a liquid resin is applied from the center to equalize the film thickness (see, for example, Patent Document 1 below).
Moreover, after applying a liquid resin, a plate-like sheet is placed and spinned to form a cover layer (see, for example, Patent Document 2 below), or a resin sheet is bonded to the liquid resin after spin-out. A technique for obtaining a resin film (see, for example, Patent Document 3 below) has been proposed.

In the technique described in Patent Document 1, a liquid resin is uniformly applied on the lid with the center portion closed, spread by spin coating, and then the lid is removed, whereby film thickness unevenness particularly in the vicinity of the center is obtained. However, since the film thickness depends on the centrifugal force of the spin-out, it is possible to reliably control the film thickness according to the condition settings such as the viscosity of the resin and the rotation speed and rotation time of the disk substrate. There was a problem that it was difficult.
In the inventions of Patent Documents 2 and 3, a plate-like sheet without holes is placed on a liquid resin film to form a resin layer having a uniform thickness integrated with the sheet. The technical idea is different from a method of forming a light transmission layer by spin-coating a liquid resin on a functional shape surface constituting an optical disk.

Further, a technique has been proposed in which a dummy substrate is placed on a liquid resin applied in an annular shape, spin-out, UV irradiation is performed, and then the dummy substrate is peeled off to obtain a cover layer (see, for example, Patent Document 4 below). However, in this technique, since glass with a release agent is used as a dummy substrate, there is a problem that the thickness of the release agent affects the thickness of the cover layer.
In order to alleviate the influence of the film thickness of the mold release agent, if the mold release agent is made thin, there is a possibility that partial island-shaped coating may occur, and there is a problem that it is impossible to sufficiently secure the mold release property. .
Further, in the technique described in Patent Document 4, a distance setting portion is provided to regulate the film thickness of the cover layer. However, the resin comes into contact with the interval setting portion on the inner peripheral side so as to be radial. There is a problem that the film does not spread evenly, or the resin comes into contact with the interval setting portion on the outer peripheral side, causing rebound into the recording area, leading to film defects such as halation.
Glass is inherently strong liquid repellency, and the release agent amplifies the liquid repellency of the glass surface, so that after the resin is shaken off, air can easily enter from the inner and outer interfaces, and the resin returns. And a recording area where no coating layer is formed occurs, and it is extremely difficult to form a uniform coating layer over the entire surface.

Furthermore, there is a problem that the device used also affects the control of the resin film.
For example, when liquid resin is applied using a barrel or valve tank, the pressure increases and fluctuates in accordance with the decrease in the internal volume, and the amount of application changes, which may cause the resin film thickness to vary. Become.
Regarding this problem, it is possible to stably control the coating amount by using a plunger pump to ensure a uniform coating width, but it is necessary to strictly control the distance between the member and the dispenser needle. That is, when these distances are closer than 0.1 mm, the tip of the dispenser needle interferes with the member due to thickness variation of the member, and there is a risk that the functional shape is damaged. On the other hand, when these distances exceed 30 mm, the resin coating width in the initial coating stage becomes large, causing a variation in the annular width, and further causing the problem that bubbles are likely to be involved.

  Still further, in the system in which the cover substrate is placed on and contacted with the liquid resin and then spun out, when the liquid resin is spread to a predetermined position and then shaken off, the gap between the cover substrate and the disk is set. In this state, air is always supplied from the central portion toward the outer periphery, and it is easy to entrain air in the curable resin, which causes the film thickness to be non-uniform.

JP-A-2005-141816 JP 2003-242694 A JP 2002-288895 A JP 2004-134050 A

As described above, when a resin film is formed by spinning out a liquid resin, it has been a conventional problem to have a uniform film thickness.
Therefore, in the present invention, the shape of the substrate and the transfer stamper is studied, and the object is to obtain a high-quality optical recording medium by making the resin film uniform by avoiding air entrainment during the resin film formation process. It was.

The present invention is a method of manufacturing a substrate for an optical recording medium having a functional shape transferred by a stamper, having a functional shape on the surface, and having an annular recess in an inner peripheral region that does not contribute to the functional shape. A step of applying a liquid resin on the stamper, a step of contacting a resin film on the liquid resin, a step of spinning out and constraining the liquid resin in the recess, and applying the liquid resin by energy irradiation. after curing, possess a step of peeling the resin film, the substrate for the optical recording medium, an inner peripheral region which does not contribute to the functional shape, has a convex portion of the annular transferred by the stamper, and The substrate for an optical recording medium , wherein the convex portion has a function of constraining the spread of the liquid resin when a coating layer is formed on the functional shape forming surface by spin coating of the liquid resin. Made of To provide a method.

According to the present invention , it is possible to reliably avoid air entering from the center hole from being mixed into the resin, and to form a high-quality transfer layer and surface coating layer excellent in film thickness uniformity and surface smoothness. The signal recording / reproduction characteristics of the medium could be improved.

  Specific examples and comparative examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Example 1]
An example of manufacturing an optical disk using the substrate and stamper of the present invention will be described with reference to FIGS.
As shown in FIG. 1 (a), an annular shape with a radius of 30 mm is set by a laser marker in an inner peripheral area from the recording area of the stamper 10 on which a predetermined pre-groove 11 is formed by photolithography, and a laser power 17A. A concentric groove having a width of 250 μm and a depth of 30 μm, that is, an annular recess 12 was formed at a scanning speed of 5 mm / sec and a laser oscillation frequency (5 kHz).
FIG. 8 shows a cross-sectional shape of the recess 12 formed by the laser marker.

Next, an acrylate monomer material (Dai Nippon Ink Die Cure Clear SD-347), which is a photocurable resin 14, is formed on the stamper 10 in an annular shape using a plunger pump (Unicontrols; Hiberpump CV). 0.6 g was applied.
Subsequently, as shown in FIG. 1B, a PC film (Pure Ace made by Teijin) 13 was placed and wetted to allow the photocurable resin to reach the concave portion 12 inside the recording area.
Then, as shown in FIG.1 (c), it shaken off for 10 seconds at 6000 rpm, and irradiated the fusion H valve | bulb for 8 seconds, and hardened resin.
At this time, since the photocurable resin 14 is constrained by the recess 12, air can be effectively prevented from entering from the interface at the center portion, and a smooth resin film without bubbles is obtained as shown in FIG. 6. .
Thereafter, as shown in FIG. 1D, the stamper 10 is peeled off at the interface to obtain a substrate for an optical recording medium in which an annular convex portion 15 is formed on the inner peripheral side that does not contribute to the recording area. It was.

Next, a process of obtaining a phase change type optical disk using the transfer substrate will be described with reference to FIGS.
As shown in FIG. 2A, a phase change recording film 21 is formed on the substrate 20 produced as described above, and then a photocurable resin 22 that is a liquid resin that is an overcoat material. In Example 2, 0.5 g of an acrylate monomer material (Dai-Cure Clear SD-318, manufactured by Dainippon Ink, Inc.) was coated in an annular shape using a plunger pump.
Next, as shown in FIG. 2 (b), the resin film 23 which is a peeling cover substrate, in this example, a PET film substrate (Toyobo Cosmo Shine A4100) is placed on the liquid and is present inside the recording area. After confirming that the photocurable resin spread to the convex portion 15, as shown in FIG. 2 (c), spinout was performed at 5000 rpm for 13 sec, and a fusion H bulb was irradiated for 10 sec to perform photocuring.
Then, by peeling at the interface between the resin film 23 and the photocurable resin 22, an optical disc having a coating layer as shown in FIG. 2 (d) was obtained.

When the optical disk manufactured by the above-described process is observed from above, as shown in FIG. 4, the innermost circumference of the photocurable resin 22 is a perfect circle and has excellent surface smoothness and film thickness uniformity. It was confirmed that a coating layer was obtained.
The phase change type optical disc as described above is initialized uniformly over the entire surface, and the recording / reproduction signal characteristics are evaluated. The focus and tracking are good, and the reflectance (RF signal) fluctuates. It was confirmed that practically sufficient characteristics were obtained.

[Example 2]
In this example, a urea resin, which is a thermosetting resin, was used as the coating layer forming material. Other than that, a phase-change optical disk was manufactured under the same conditions as in Example 1 above.
A substrate was produced according to the steps of FIGS. 1 (a) to (d), and a coating layer was formed according to the steps of FIGS. 2 (a) to (d). That is, when the thermosetting resin reached the concentric convex portions 15, the thermosetting resin was cured by shaking off at 5000 rpm for 20 seconds and heating at 160 ° C. for 30 minutes. Then, the coating layer was obtained by peeling the thermosetting resin 22 and the PET film substrate 23.
When the optical disk manufactured by the above-described process is observed from above, as shown in FIG. 4, the innermost circumference of the photocurable resin 22 is a perfect circle and has excellent surface smoothness and film thickness uniformity. It was confirmed that a coating layer was obtained.
The phase change type optical disc as described above is initialized uniformly over the entire surface, and the recording / reproduction signal characteristics are evaluated. The focus and tracking are good, and the reflectance (RF signal) fluctuates. It was confirmed that practically sufficient characteristics were obtained.

Example 3
In this example, a process of manufacturing a stamper in which concentric grooves are formed in the inner periphery from the pregroove and the recording area by photolithography will be described with reference to FIGS.
First, as shown in FIG. 3A, a negative resist (SU-8 manufactured by Microchem) 31 is applied to a glass substrate 30 to a thickness of 10 μm, and after drying, mask exposure is performed only at a position of 30 mm in diameter.
Next, as shown in FIG. 3B, development processing is performed using a predetermined solvent (Micro Chem SU-8 developer), and concentric convex portions having a width of 100 μm and a height of 10 μm are formed on the glass substrate 30. 32 was formed.
Next, as shown in FIG. 3C, a positive resist (TSMR-8900 manufactured by Tokyo Ohka Kogyo Co., Ltd.) 33 is applied to the outside of the convex portion 32, that is, outside the position of 30 mm in diameter, and dried, The DVD format is exposed by laser drawing.
Next, as shown in FIG. 3 (d), by performing development with a TMAH (tetramethylammonium hydroxide) aqueous solution (DE-3 manufactured by Tokyo Ohka Kogyo Co., Ltd.), a DVD having a track pitch of 0.74 μm and a depth of 30 nm is obtained. A pregroove 34 is formed.
Next, as shown in FIG. 3E, concentric grooves having a width of 100 μm and a depth of 10 μm, that is, a recess 12 are formed inside the recording area by Ni electroforming after sputtering metallization, glass substrate, and back surface polishing. The stamper 10 thus obtained was obtained.

Using this stamper 10, a substrate for an optical disk was produced, and by forming a predetermined recording layer and coating layer, an optical recording medium having good focus and tracking and excellent reproduction signal characteristics was obtained.

[Comparative Example]
In this example, transfer was performed using a conventionally known stamper having no recess in the inner peripheral region to prepare a substrate, and an optical disk was manufactured using this.
When the optical disk was observed from above, as shown in FIG. 5, the innermost circumference of the spreading resin of the coating layer formed on the recording layer did not become a perfect circle. In the spin-out process, air was mixed from the interface at the central portion, and bubbles were generated in the film as shown in FIG.

(A)-(d) The manufacturing process figure of the board | substrate for optical recording media of this invention is shown. (A)-(d) The manufacturing process figure of the optical disk using the board | substrate of this invention is shown. (A)-(d) The manufacturing process figure of the stamper for board | substrate transcription | transfer of this invention is shown. A schematic top view of an optical disc produced by the method of the present invention is shown. The schematic top view of the optical disk produced using the conventionally well-known stamper is shown. The state of the coating layer of the optical disk produced using the stamper of this invention is shown. The state of the coating layer of the optical disk manufactured using the conventionally well-known stamper is shown. The cross-sectional shape of the recessed part which comprises the board | substrate of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Stamper 11 Pregroove 12 Concave 14 Photocurable resin 13 PC film 15 Convex part 20 Substrate 21 Phase change recording film 22 Photocurable resin 23 Resin film 30 Glass substrate 31 Negative resist 32 Convex part 33 Positive resist 34 Pregroove

Claims (1)

A method of manufacturing a substrate for an optical recording medium having a functional shape transferred by a stamper,
Applying a liquid resin on a stamper having a functional shape on the surface and having an annular recess in an inner peripheral region that does not contribute to the functional shape;
Contacting the resin film on the liquid resin;
Spinning out and constraining the liquid resin in the recess;
After curing the liquid resin by the energy irradiation, it possesses a step of peeling the resin film,
The substrate for the optical recording medium has an annular convex portion transferred by the stamper in an inner peripheral region that does not contribute to the functional shape, and the convex portion is formed with the functional shape by spin coating of a liquid resin. A method for producing a substrate for an optical recording medium, which has a function of constraining the spread of the liquid resin when a coating layer is formed on the surface .