JP2507048B2 - Optical disc master manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a master such as a high density optical disc having a small crosstalk and a high SN ratio.

Conventional technology Generally, an optical disk master is manufactured by a series of steps including resist coating, optical cutting, development, etching, and resist removal. As one of the etching treatment methods in the process, an ion beam using an ion gun is used. Etching is being performed.

With the minimum pit area and track pitch of the conventional optical disk, there is no problem in terms of crosstalk and SN ratio even if the ion beam generated from the ion gun is used as it is for etching. For example, in order to further reduce crosstalk between adjacent tracks, it is necessary to make the side surfaces of the pits perpendicular to the disk surface, and ion beam etching, which has less side etching and tends to have anisotropy, is effective. Is.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the present optical disc, the pit area of the minimum pit is very small, about 0.4 μm × 0.6 μm. Therefore, when the track pitch, which was about 1.6 μm in the past, is narrowed to 1 μm or less, the crosstalk becomes large in the optical disc manufactured by the above conventional manufacturing method.

It is possible to obtain a more standing pit by blocking a beam component from an oblique direction with respect to the pit and etching with an ion beam having a high directivity. However, the bottom surface of the pit, which is the etching surface, becomes rough, scattering increases, and the SN ratio deteriorates.

It is an object of the present invention to provide a method for manufacturing an optical disk master that can solve the conventional problems as described above.

Means for Solving the Problems In a method for manufacturing an optical disk master, resist coating,
In front of the master that has been subjected to optical cutting and development processing,
A mask for reducing a beam incident component from an oblique direction is attached, and an etching is performed by irradiating the master with an ion beam from a substantially vertical direction. After that, the photoresist is removed, and surface treatment is performed by ion irradiation with low energy.

By reducing the incidence of the ion beam from the oblique direction by attaching the mask, the side surface of the pit can be etched perpendicularly to the master. Further, since the etching rate of a photoresist for a beam with a high incident angle is generally higher than that of a metal, by shielding the high incident angle component with a mask, a sufficient etching rate difference between the master metal and the photoresist can be obtained, and coating should be performed. It is possible to reduce the thickness of the photoresist.

Further, by irradiating low energy ions after removing the photoresist, it is possible to reduce the roughness of the master surface due to ion beam etching.

Example Hereinafter, a method of manufacturing an optical disk master according to an example of the present invention will be described.

As shown in FIG. 1A, a mask 3 for blocking a high incident angle component of the ion beam 2 emitted from the ion gun 1.
Is mounted in front of the master 4 on which resist coating, optical cutting and development have been performed, and while the master 4 is rotated, the ion beam 2 is vertically irradiated to perform etching. The shape of the opening of the mask 3 depends on the diameter of the ion gun 1 and the size of the master 4. Further, it is necessary to change the shape of the opening according to the beam profile, rather than changing it into a simple fan shape.

By performing the above-mentioned processing, the master 4 can be uniformly irradiated with the ion beam 2 from the vertical direction, and the pits 5 can be compared with the case where the mask 3 is not used (FIG. 2A). A pit 5 having a raised side surface is obtained (FIG. 2 (b)). As an example of etching conditions when Ar gas which is an inert gas is used, the ion energy is
500eV, ion current density on the master surface is 0.3mA / cm
^{At 2} , the mask rate of 60 ° opening was used and the etching rate was about 3 nm / min.

When recording pits 5 on a master 4 using Cu that has been V-grooved in advance, the wavelength used as a read head is
If a 780 nm laser is used, the depth of pit 5 is about 1
30 nm (= 1/4 nλ) is required. AZ1350 for photoresist
When J (manufactured by Shipley) is used and the mask 3 is not used, the etching rate ratio between Cu and AZ1350J is approximately 1: 1 and it is necessary to apply photoresist to the V groove crests with a thickness of 130 nm or more. There is. However, if the photoresist is too thick, problems will occur in terms of recording laser intensity and tracking, so the resist thickness is preferably 100 nm or less.
By using the mask 3 as described above, the high incident angle component is reduced, a sufficient etching rate difference between the master 4 metal and the photoresist can be obtained, and etching with a thin resist thickness and a sufficient depth is performed. It becomes possible.

After removing the resist from the master 4 that has been subjected to the etching process,
Surface treatment by low energy ion irradiation. As shown in FIG. 1 (b), the master 4 with the resist removed,
Alternatively, one of the ion guns 1 is tilted so that the ion beam 2 is set to enter the master 4 from an oblique direction, and the master 4 is irradiated with low-energy ions 2 while being smoothed. . This roughness is a result of performing ion beam etching from a single direction, and it is considered that there is a difference in etching rate depending on the crystal direction of the master 4 metal. When Cu is used for the master 4 metal, the degree of roughness is 10 to 30% of the etching amount, and the higher the ion energy, the worse the roughness.

The irradiation of the ion beam 2 was performed under the vacuum of 2 × 10 ⁻⁴ Torr using Ar gas under the conditions of an ion beam voltage of about 300 V and an incident angle of 60 °. However, if the vacuum degree is 2 × 10 ^-3 Torr or less, there is no problem, and the beam voltage may be 500 eV or less. The incident angle θ may be appropriately selected within the range of 45 ° ≦ θ (≦ 90 °).

In addition, the irradiation of low energy ions described above,
It is also effective as a method for removing the burrs 6 formed around the pits 5 or around the groove edges by reattaching the etched particles to the master 4.

The burr 6 formed around the pit 5 is shown in FIG. 3 (a).
As shown in FIG. 4B, the signal pits 5 having a lower frequency are more likely to be formed in the portion along the circumference of the master 4, so that as shown in FIGS. 4A and 4B, from the radial direction of the master 4. It is effective to irradiate the ion 2 at a high incident angle. By this treatment, the bottom surface of the pit 5 can be made smooth, and at the same time, the burrs 6 formed around the pit 5 or at the groove periphery can be removed.

Further, in the case of the master 4 in which pits are formed by ion beam etching on the slope of the V groove of the master 4 which has been V-grooved along the circumference in advance, the shape of the V groove is impaired by the above-described method. From the tangential direction of the V groove as shown,
By irradiating the ion 2 with a high incident angle to V
It is possible to smooth the bottom surface of the pit 5 while maintaining the shape of the groove, and at the same time, remove the burr 6 formed around the pit 5 or on the peripheral edge of the groove.

EFFECTS OF THE INVENTION In the method for manufacturing an optical disk master according to the present invention, low energy ions are obtained after removing the photoresist by performing ion beam etching from a substantially vertical direction on the master subjected to resist coating, optical cutting, and development processing. By performing the surface treatment by irradiation, it is possible to form a pit having a sufficient depth in which the side surface of the pit is perpendicular to the master and to manufacture a smooth master having no surface roughness.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) show a method for manufacturing an optical disk master according to an embodiment of the present invention, and FIG. 1 (a) is a side view showing a step of irradiating the master with an ion beam in a vertical direction,
2B is a side view showing the step of irradiating the master with an ion beam in an oblique direction, and FIG. 2A is a cross-sectional view of the master surface of the optical disc when the mask of the embodiment is not used. FIG. 3 (b) is a cross-sectional view of the surface of the optical disc master using the same mask, and FIGS. 3 (a) and 3 (b) are plan views (a) and cross-sectional views (b) showing burrs formed around the pits. 4 (a) and 4 (b) are a plan view (a) and a side view (b) showing an ion irradiation step from the radial direction in the same embodiment, and FIGS. It is the top view (a) and side view (b) which show the ion irradiation process from the direction. 1 ... ion gun, 2 ... ion beam, 3 ... mask,
4 ... Disk master.

Claims (5)

(57) [Claims] 1. In a method of manufacturing an optical disk master, when etching a master that has been subjected to resist coating, optical cutting, and development treatment, first, the master is irradiated with an ion beam in a direction substantially perpendicular to the etching, and photo etching is performed. A method for manufacturing an optical disk master, which comprises performing surface treatment by low energy ion irradiation after removing the resist. 2. The method of manufacturing an optical disc master according to claim 1, wherein the surface treatment by low energy ion irradiation is performed by an ion beam having an ion beam with a high incident angle as a main component. 3. The method of manufacturing an optical disk master according to claim 2, wherein the surface treatment by low energy ion irradiation is applied to the master in a radial direction. 4. The method for manufacturing an optical disk master according to claim 2, wherein the surface treatment by low energy ion irradiation is applied to the master in a circumferential direction. 5. The method of manufacturing an optical disc master according to claim 4, wherein V-groove processing is performed on the optical disc master in advance.