KR20080023476A - Manufacturing method of stamper for optical recording medium - Google Patents

Abstract

A method for manufacturing a stamper for an optical recording medium is provided to increase the density of a master substrate by using a phase change material as a photoresist. A method for manufacturing a stamper for an optical recording medium comprises the steps of: coating a phase change photoresist(42) on a master substrate(41); phase-changing the photoresist by emitting laser; developing the photoresist; depositing a metal layer; and separating the metal layer. The photoresist developing step includes a step of dipping the master substrate in alkali solution selected one of NaOH, KOH, and LiOH.

Description

Manufacturing method of stamper for optical recording medium {Manufacturing method of stamper for optical recording medium}

1 shows a method of recording and reproducing information using a conventional optical recording disc.

2 shows a phase change state between crystalline and amorphous phase when the phase change material is irradiated with a laser.

3 shows the difference in patterning in the conventional optical mode and pattern formation in the thermal mode according to the present invention.

4A to 4D show a method of manufacturing a master disc in the thermal mode according to the present invention.

5A and 5B illustrate a method of forming a stamper 45 from a patterned master substrate.

※ Description of main part of drawing ※

31: objective lens 32: recording layer

33: substrate 34,35: graph

36,37: spot

41: master substrate 42: inorganic photoresist

43 pattern 44 electroless plating layer

45: plating layer

The present invention relates to a master disc and a stamper manufacturing method for use in the manufacture of an optical recording medium. More specifically, the present invention uses a phase change material as a photoresist in the pattern formation of the master mode used in the manufacture of a high density optical recording medium, thereby providing a master disc having a more sophisticated pattern by exposure by heat instead of exposure by light. And a stamper manufacturing method.

The present invention relates to a method for manufacturing a master disk and a stamper capable of implementing a 100 GB / disc capacity applicable to a near field recording method by using a laser beam recorder (LBR) capable of implementing a capacity of about 25 GByte / disc. As such, the master disk is patterned using an inorganic photoresist.

Recently, with the demand for high-density recording media, next-generation recording systems such as the near-field recording method and the super-RENS method have been studied. There is a master disk containing the pattern to be formed, a stamper is produced from the master disk, and the disk substrate is injection molded using the stamper to obtain an optical recording disk, by coating the recording layer and the protective layer. You will get the final optical recording disc.

The conventional master disk is manufactured through the following process.

After the coupling agent is applied to the glass substrate or the circular substrate made of polycarbonate, the photoresist is uniformly applied to an appropriate thickness.

The laser is focused and patterned on the surface of the photoresist-coated disk. In this process, patterning is performed using a device called a laser beam recorder (LBR). The density of the optical disk is determined by the laser wavelength and the numerical aperture of the optical system. That is, the size of the pattern to be patterned is determined.

The development of the exposed portion by applying a developer onto the patterned disc completes the patterning of the master disc.

A thin metal film is formed on the surface of the patterned master disk by electroless plating. Then, the master disk disc with electroless plating is placed in a nickel sulfate plating bath to grow a nickel plating layer by an electroplating method.

The stamper is completed by separating the nickel plating layer from the master disk. The protective film is applied to the stamper, the inner and outer diameters required for injection molding are cut, and the final optical recording disc is manufactured through the injection molding process.

On the other hand, Fig. 1 shows a method of recording and reproducing information by using the optical recording disc finally produced. The optical recording disc is formed by forming a recording layer 12 on a glass or silicon substrate 11 and forming a cover layer 13 on the recording layer 12 to protect the recording layer 12 thereon.

Blue laser light having a wavelength of 405 nm is focused using the objective lens 14 having NA 0.85, which first passes through the cover layer 13 and then reaches the recording layer 12.

In the case of the optical recording disk according to the prior art, the recording density is related to the size of the focused laser light, which is determined by the wavelength of the light source and the NA of the lens used in consideration of the diffraction of the laser light. According to the Rayleigh diffraction limit, the diameter D of the focused laser light is

However, the practically available limit may be regarded as 0.61, which is a coefficient corresponding to a full width at half maximum of a laser light having a Gaussian intensity distribution. Therefore, in order to increase the recording density by reducing the pattern size, the wavelength of the laser may be reduced or the NA of the lens may be increased. However, there is a limit in the reduction of the laser wavelength, and the increase of NA is accompanied by difficulty in servo control and increase in aberration.

The smallest mark that can be practically obtained using a blue wavelength and an optical system of NA 0.85 is about 150 nm in diameter, has a density of 18 Gigabits per square inch, and the total capacity of one disk is 25 GBytes.

The capacity of the optical disc is the same as that of the master disc for manufacturing it, and in order to manufacture a high capacity optical recording disc, the capacity of the master disc must also be high. When manufacturing the master disc, using the conventional technique as described above, the shortest laser wavelength available in LBR so far is about 250 nm in Deep UV, and the maximum capacity that can be obtained even by patterning with such a laser is As with the final product, the optical disc is 25 GByte / disc.

The most basic cause of the maximum capacity limit may be viewed as the wavelength of the laser, but the actual cause is that the photoresist reaction is caused by the photon mode when UV laser is irradiated to the organic photoresist (photoresist). This is because.

That is, when the pattern is formed after development, since the pattern is formed in the entire area where the laser beam is irradiated and the light reaches, there is a limit in reducing the size of the pattern. Therefore, there is a limit to achieving a capacity of 25 GByte or more in the method using the LBR as in the conventional method. In addition, the recording / reproducing process after disc production is limited to 25 GByte in the conventional optical system as shown in FIG.

Therefore, in order to manufacture a disk having a capacity of 25 GByte or more, a master disk having a larger capacity is required, and for this, a new method of manufacturing a master disk is required.

It is an object of the present invention to provide a method capable of manufacturing a high density master substrate using a more precise laser spot.

In addition, the master substrate manufacturing method of the present invention aims to provide a master manufacturing method that can be combined with a new recording method such as the recent near field recording method to produce a higher density disk.

The master patterning method according to an embodiment of the present invention comprises the steps of applying a phase change photo resist to the master substrate; Irradiating a laser to phase change the photoresist; And developing the photoresist.

Stamper manufacturing method according to an embodiment of the present invention, the step of applying a phase change photo resist to the master substrate; Irradiating a laser to phase change the photoresist; Developing the photoresist; Depositing a metal layer; And separating the metal layer.

Master substrate according to the present invention, a circular substrate; And a phase change photoresist applied on the substrate.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

2 shows a phase change state between crystalline and amorphous phase when the phase change material is irradiated with a laser.

In a so-called phase change disk in which such a phase change material is applied to the recording layer of the disk, the recording layer is irradiated with a laser so that the portion to which the laser is irradiated is crystalline from amorphous to amorphous, or On the contrary, the phase change occurs, and the portion where the phase change has occurred and the portion where the phase change has not occurred represent '0' and '1', respectively, to record data.

In the case of a phase change material, a phase is determined according to an atomic arrangement form as shown in FIG. 2. The crystalline phase is when the atoms are located at each lattice point and the entire solid is in a low energy state.Then, after melting, it is quenched to keep the atoms from entering each lattice point. If not, it is called an amorphous phase.

Phase change between crystalline and amorphous occurs depending on the temperature applied and the heating or cooling time. In other words, when the crystalline solid is melted at a temperature of about 600 ° C. or higher with a high-temperature laser beam and quenched, it becomes amorphous. When the solid is heated at a crystal temperature at a temperature of about 200 ° C. or more, the crystal becomes crystalline.

In the present invention, unlike the mastering process by the photon mode in which the photosensitive organic photoresist is irradiated with a laser to perform patterning, an inorganic photoresist, which is a material causing a phase change according to the process, is used. In addition, the laser is irradiated to the inorganic photoresist to perform mastering in a thermal mode in which a pattern is formed through phase change.

3 shows the difference in patterning in the conventional optical mode and pattern formation in the thermal mode according to the present invention.

The master disc is composed of a silicon or glass substrate 33 and a recording layer 32 applied thereon. The laser passes through the objective lens 31, focuses on the surface of the recording layer 32, and the portion of the recording layer 32 to which the laser is irradiated produces a phase change from crystalline to amorphous or vice versa. To form. That is, depending on whether the recording layer 32 is applied in a crystalline state or in an amorphous state, the state of the crystal constituting the pattern may vary.

As shown in Fig. 3, the graph 34 shows the temperature profile in the light mode when the laser light is irradiated to the organic photoresist, and the graph 35 shows the laser light to the phase change inorganic photoresist. That is, the temperature profile in thermal mode. The spot 37 is formed in the area | region which becomes more than predetermined temperature profile in an organic photoresist or an inorganic photoresist.

The area where the organic photoresist is exposed to form a pattern by irradiating the laser light is distributed over a relatively wider area as shown in graph 34, and the temperature profile when patterned by heat is compared with the graph 35. Likewise distributed over a narrower area.

Therefore, the size of the spot 37 formed by the optical mode becomes larger than the size of the spot 36 formed by the thermal mode, and thus patterning the master disk into small spots that can be formed by the thermal mode. In this way, smaller pit or grooves can be patterned on the master disk, and the master disk can be patterned more precisely.

For patterning by the thermal mode according to the present invention, instead of the conventional photosensitive photoresist, an inorganic photoresist which causes a phase change by an appropriate threshold temperature is used. Preferably, a phase change material such as GeSbTe may be used as the inorganic photoresist. The phase change material is not limited to the inorganic photoresist and may be used as long as it can cause phase change by a laser and has a proper property.

4A to 4D show a method of manufacturing a master disc in the thermal mode according to the present invention.

As shown in FIG. 4A, an inorganic photoresist 42 capable of phase change is applied to the master substrate 41. As the inorganic photoresist 42, a phase change material such as GeSbTe may be used. As the master substrate 41, silicon, polycarbonate, or an organic substrate may be used.

As shown in FIG. 4B, the inorganic photoresist 42 of the portion to be patterned is irradiated with a laser to change phase. When GeSbTe is used as the inorganic photoresist 42 and coated in a crystalline state, the laser is irradiated to a portion to be patterned, melted at about 600 ° C. or more, and then quenched to change to an amorphous state to form a pattern. In the case where GeSbTe is used as the inorganic photoresist 42 and coated in an amorphous state, the laser is irradiated to a portion to be patterned, and when heated at a temperature of about 200 ° C. or more for a time necessary for crystallization, the pattern is changed to a crystalline state to form a pattern. do.

In the following embodiment, a case where the inorganic photoresist 42 is applied in an amorphous state will be described as an example. In this case, as shown in FIG. 4B, when the laser is irradiated to the portion to be patterned, the pattern 43 is in a crystalline state.

Subsequently, when the substrate is immersed in the alkaline developer, as shown in Fig. 4C, the portion of the pattern 43 in the crystalline state is blown away, leaving only the portion in the amorphous state to form the pattern of the master substrate. In this case, only the portion irradiated with the laser is removed, which is an intaglio pattern of a pattern to be formed on the final disk.

When the inorganic photoresist 42 is applied in a crystalline state, only the portion to which the laser is irradiated remains, so that a pattern identical to the pattern to be formed on the final disk is formed on the master substrate 41.

At this time, an alkaline solution is used as the developer used for development, for example, NaOH, KOH, LiOH, or the like may be used. Among them, NaOH can obtain the most suitable selectivity at a specific concentration.

The selectivity of development refers to the difference in the degree of etching between amorphous and crystalline in the same developer, and when developing after phase change of the part corresponding to the pattern with a laser, the portion 43 that is developed and removed after development, that is, crystalline This can be seen through the depth of the part.

The selectivity may vary depending on the concentration of the developer. 6A-6C show the change in permeability of phase change inorganic photoresist in crystalline and amorphous states over time for three NaOH concentrations. That is, the change in transmittance will vary according to the degree of development, and in particular, the difference in permeability between amorphous and crystalline directly indicates the selectivity.

The initial phase change inorganic photoresist is 50 nm thick. 6A-6C show the change in permeability over time when the concentration of NaOH is 0.4%, 1%, and 4%, respectively.

In the case of 0.4% of Fig. 6A, the etching seems to start, but the etching rate is too slow, which is not good. In the case of 4% of FIG. 6C, the problem of development speed is not seen, but as time passes, the photoresist in the amorphous state is also developed, resulting in a change in transmittance.

On the other hand, when the concentration is 1% in Fig. 6B, the development speed is not only applicable to the actual process, but it can be seen that there is almost no change in the amorphous transmittance.

In the embodiment of the present invention, when GeSbTe is used as the phase change inorganic photoresist 42, NaOH is preferably used as the developer, and the concentration thereof is preferably 0.5 to 3%, more preferably about 1 % to be.

More preferably, when the phase change inorganic photoresist 42 is dipped in the developer, ultrasonic waves are applied together. By applying ultrasound, the selectivity of the phenomenon can be improved by 30% or more.

5A and 5B illustrate a method of forming a stamper 45 from a patterned master substrate.

As shown in Fig. 5A, a thin electroless plating layer 44 is formed on the master substrate of Fig. 4C by electroless plating, and the electroless plating is carried out by placing a master substrate on which electroless plating is carried out in a nickel sulfate plating bath. Grow 45. Then, as shown in Fig. 5B, when the nickel plating layer 45 is separated from the master disk, it becomes a stamper.

Thereafter, a protective film is applied to the stamper, the inner and outer diameters required for injection molding are punched out, and a final optical recording disc is manufactured through the injection molding process.

According to the master substrate manufacturing method of the present invention it is possible to manufacture a high density master substrate using a more precise laser spot.

The method of manufacturing a master substrate of the present invention is also applied to manufacturing a disk for an optical system using SIL (Solid Immersion Lens), which is one of near field recording methods, and thus can be applied to manufacturing a disk substrate of higher capacity.

Claims (12)

Applying a phase change photo resist to the master substrate; Irradiating a laser to phase change the photoresist; And Developing the photoresist; Master patterning method comprising a. The method of claim 1, Developing the photoresist, And dipping the substrate into an alkaline solution. The method of claim 2, The alkali solution is a master patterning method, characterized in that any one of NaOH, KOH, LiOH solution. The method of claim 3, The concentration of NaOH is a master patterning method, characterized in that 0.5 to 3%. The method of claim 2, Developing the photoresist, And applying an ultrasonic wave during the development. Applying a phase change photo resist to the master substrate; Irradiating a laser to phase change the photoresist; Developing the photoresist; Depositing a metal layer; And Separating the metal layer; Stamper manufacturing method comprising a. The method of claim 6, Developing the photoresist, And dipping the substrate in an alkaline solution. The method of claim 7, wherein The alkali solution is a stamper manufacturing method, characterized in that any one of NaOH, KOH, LiOH solution. The method of claim 8, The concentration of NaOH is a stamper manufacturing method, characterized in that 0.5 to 3%. The method of claim 6, Developing the photoresist, Stamper manufacturing method characterized in that it further comprises the step of applying ultrasonic waves during the development. The method of claim 6, Depositing the metal layer, Electroless plating; And Growing the electroless plating layer by electroplating; Stamper manufacturing method comprising a. Circular substrates; And And a phase change photoresist applied on said substrate.

Images