JPH04325943A - Production of optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the high-density optical recording medium by etching the inorg. film on a glass original plate twice by a laser beam, then transferring the etched parts onto a metallic plate and further transferring these parts to plastic. CONSTITUTION:The inorg. film 2 consisting of a metal or silicon, or silicon oxide or silicon nitride of a prescribed thickness is formed on the glass original disk 1. A photoresist 3 is then applied and is formed with exposed parts 4 by using a laser cutting machine. The parts are then developed to form the etched parts 5. The photoresist 3 playing the role of the mask of the inorg. film 2 is removed and again the photoresist 3 is applied thereon. The exposed parts 4 are formed by the laser cutting machine. The aligning of the exposing beam is executed by using the grooves or pits on the inorg. film 2 formed in the previous stage at this time. The etched parts 5 are then formed. This etching is executed down to the depth varying from the depth of the previous stage. A fine stamper is formed in such a manner.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for forming track guide grooves of an optical recording medium or pits for recording preformat signals at a higher density.

0002

[Prior Art] Optical recording media uses a semiconductor laser as a light source, and uses a lens to focus light with a wavelength of 780 to 830 nanometers into a spot of 1 to 2 micrometers to reproduce information. recorded or erased. On this optical recording medium, track guide grooves for guiding a laser spot for recording and reproduction to tracks where information exists, or pits in which information is recorded in advance are formed.

[0003] Optical recording media are manufactured by making a mold (stamper) for manufacturing the substrate in a process called mastering, manufacturing a plastic substrate using the stamper and injection molding method, and then coating the substrate with a recording film, a reflective film, etc. It is manufactured by forming a film. Among these, the mastering process according to the present invention involves coating a glass original plate with photoresist, exposing the photoresist to light using a device called a laser cutting machine, developing the exposed area, and forming the track guide groove of the optical recording medium.
Alternatively, there is a method of manufacturing a stamper by forming preformat signal pits and transferring them to a metal plate using electroforming.

A method of manufacturing an optical recording medium using a substrate, a metal film on the substrate, and a photoresist is disclosed in Patent Application Publication No. 56-52361. In addition, a method using only photoresist is a patent application published in 1986-50.
733.

[0005]

In the methods currently used in mastering processes, the width of the grooves or pits on the stamper to be produced is largely dependent on the diameter of the laser beam of the laser cutting machine. However, when the wavelength of a laser beam for reproducing or recording an optical recording medium becomes shorter and a higher-density optical recording medium becomes necessary, the current mastering process cannot cope with this problem.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art by forming finer grooves or pits and forming grooves or pits of different depths and widths on the same optical recording medium. An object of the present invention is to provide a method for manufacturing an optical recording medium in which pits are formed.

[0007]

[Means for Solving the Problems] The present invention involves forming an inorganic film of metal, semiconductor, oxide, or nitride on a glass original plate, applying a photoresist on the inorganic film, and applying the photoresist to the inorganic film. exposing a resist to a laser beam; developing the photoresist exposed to the laser beam to remove the exposed portion; etching the inorganic film exposed by removing the exposed portion of the photoresist; a first step of removing the photoresist to form grooves or pits in the inorganic film; and applying a photoresist on the inorganic film that has undergone the first step; While aligning the exposure laser beam using the formed grooves or pits, the same exposure and development processes as in the first step are performed, and the inorganic film is etched again, thereby completing the first step. A groove formed by a groove, or a groove having a width or depth different from that of a pit,
Alternatively, through a second step of forming pits, the grooves,
Alternatively, the pits are transferred to a metal plate by electroforming, and the grooves or pits are further transferred to plastic using the metal plate as a mold.

Further, the laser beam for exposing the photoresist is a light having a distribution in which the intensity is highest at the center of the laser beam and the intensity decreases toward the periphery of the laser beam, and the exposure width of the photoresist is It is characterized in that the photoresist is exposed so that the laser beam incident surface side is wide and the surface side in contact with the inorganic film is narrow.

[0009] Furthermore, the intensity distribution within the laser beam has a substantially Gaussian distribution, and the mask or prism placed in the path of the laser beam
The intensity distribution of the spot focused on the photoresist by the lens has large side lobes, and the width of the main spot is narrower than in the case without the mask or prism.

[0010] Also, a photoresist is coated on a silicon substrate, the photoresist is exposed to a laser beam, the photoresist exposed to the laser beam is developed to remove the exposed portion, and the photoresist is further exposed to light by a laser beam. a first step of etching the silicon substrate exposed by removing the exposed portion of the resist, and then removing the photoresist to form a groove or pit in the silicon substrate; A photoresist is applied on the silicon substrate, and the same exposure and development processes as in the first step are performed while aligning the exposure laser beam using the grooves or pits formed in the first step. The silicon substrate is then etched again to form grooves or pits having a width or depth different from the grooves or pits formed in the first step, and then the grooves are etched. Alternatively, the pits are transferred to a metal plate by electroforming, and the grooves or pits are further transferred to plastic using the metal plate as a mold.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a process diagram showing a method for manufacturing an optical recording medium according to the present invention, and the steps are performed in the order of (a) to (h). 1 is a glass original plate, and first, in step (b), an inorganic film such as metal, silicon, silicon oxide, or silicon nitride is formed on the glass original plate to a predetermined thickness. Next, in step (c), a photoresist is applied onto the original plate. In step (d), the photoresist is exposed using a laser cutting machine, and the exposed areas are developed and removed. In step (e), the inorganic film under the photoresist is removed by etching, but the etched portions are limited to the exposed areas of the photoresist. In step (f),
The photoresist that served as a mask for the inorganic film is removed, and photoresist is applied again in step (g). (
In step h), the photoresist is exposed using a laser cutting machine as in step (d), but at this time, the exposure beam is aligned using the grooves or pits on the inorganic film formed in the previous step. . In (i), (h
) The inorganic film is etched using the exposed photoresist as a mask. Etching in this step can be performed to a different depth than in the previous step (e).

FIG. 2 is a process diagram showing another method of manufacturing an optical recording medium according to the present invention, in which the steps are performed in the order of (a) to (h). 8 is a silicon substrate, and first, in the step (b), a photoresist is applied onto the silicon substrate. In the step (c), the photoresist is exposed using a laser cutting machine, and the exposed areas are developed and removed. In the step (d), the silicon under the photoresist is processed by etching, but the etched portion is limited to the area where the photoresist is exposed. Further, the etching is stopped when a desired groove or pit depth is reached. In the step (e), the photoresist serving as a mask is removed, and in the step (f), photoresist is applied again. In the step (g), (c
), the photoresist is exposed using a laser cutting machine, but at this time, the exposure beam is aligned using the grooves or pits on the inorganic film formed in the previous process. In step (h), the inorganic film is etched using the photoresist exposed in step (g) as a mask. Etching in this step can be performed to a different depth than in the previous step (d).

FIG. 3 shows the process of making a stamper in the steps shown in FIGS. 1 and 2, in which (a) and (b) are when a glass original plate is used, and (c) and (d) are when a silicon substrate is used. This corresponds to the case where In (a) and (c), a metal film is formed on each surface to make it conductive, and then a metal such as nickel is grown by electroforming, and the metals that are electroformed in (b) and (d) are A stamper is produced by peeling off the stamper.

When performing laser cutting, if the intensity distribution of the laser beam focused on the photoresist is made to have a Gaussian distribution shape as shown schematically in Figure 4(a), the photo exposed by this beam will be The cross section of the resist has a range as shown in FIG. Therefore, if the beam shape is such that the light intensity is highest at the center and gradually decreases at the periphery, as shown in FIG. , can be made smaller on the other side. As shown in Figure 5, after removing the exposed portion by development processing, etching the inorganic film 2 using the photoresist 3 as a mask, it is possible to form irregularities in the inorganic film according to the pattern of the laser exposure. However, the width of this pattern is smaller than the width of the laser beam used for exposure.

When a laser beam is focused using a lens, the spread of the spot at the focal point is determined by the wavelength of the laser and the numerical aperture of the lens. Therefore, it is difficult to narrow the range in which the photoresist is exposed. However, if a slit is inserted in the optical path in front of the objective lens 11 as shown in FIG. 7(a), or a prism is inserted as shown in FIG. 7(b) and only the peripheral part of the objective lens is used, the intensity distribution at the focal point can be transformed into a shape with relatively large side lobes and a narrow main spot, as shown in FIG. 4(b).

When the intensity distribution of the laser beam focused on the photoresist is shaped as shown in FIG. 4(b), the cross section of the photoresist exposed by this beam is as shown in FIG. The range will be as shown. Therefore, even if the light intensity distribution has large side lobes as shown in Figure 4(b), if the intensity is adjusted to a range where the entire thickness of the photoresist is not exposed in the side lobes, only the narrow main spot can be exposed. exposes the bottom of the photoresist. After all, the etching width of the inorganic layer under the photoresist can be controlled by the width of the main spot. Figure 6 (a
) As shown in Figure 6, after removing the exposed portion by development processing, the inorganic film in 2 is etched using the photoresist in 3 as a mask.The area shown in 5 in Figure 6 is etched, and the pattern formed by laser exposure on the inorganic film is etched. However, the width of this pattern is smaller than the width of the laser beam used for exposure. FIG. 6(b) shows a case where the substrate is a silicon substrate. In this case, unevenness can be formed on the wafer by stopping etching at a predetermined depth.

By utilizing this fact, it becomes possible to freely form a stamper having a finer pattern than the laser beam width of the laser cutting machine. Furthermore, the interval between patterns can also be made equal to or less than the laser beam width. Figure 5(b) shows an example of this. The exposed areas of the photoresists in No. 3 overlap on the laser beam incident side, but the exposed areas are separated on the inorganic film side, so the etching of the inorganic film does not occur. Part diagram 5
5 in (b) can be formed completely separately. Although the inorganic film is etched completely to the glass original plate in FIG. 5(b), the etching may be stopped midway. In that case, it will be similar to the case where a silicon substrate is used.

(Example 1) A silicon thin film of 80 nanometers was formed by sputtering on a glass original plate having a thickness of 10 mm and a diameter of 200 mm. A photoresist was applied onto this silicon thin film to a thickness of 120 nanometers by spin coating, and fixed by baking. The glass original plate on which the silicon thin film and photoresist layer have been formed is placed on a laser cutting machine, and a laser beam with a wavelength of 442 nanometers is focused by an objective lens with a numerical aperture of 0.9 and focused onto the photoresist. Exposure was performed in a spiral manner at a micrometer pitch. Next, the exposed portion of this photoresist was developed and removed, and then the silicon thin film was etched by reactive ion etching to form a groove with a depth approximately half the thickness of the silicon film.

Once again, a layer of photoresist is applied on the silicon film.
It was coated to a thickness of 20 nanometers and exposed using a laser cutting machine. In this exposure process, using the grooves previously formed on the silicon film as a guide, exposure was performed to form pits between the grooves. The pit spacing was set to 1 micrometer at the narrowest part. After developing the photoresist, etching was performed to cover the entire thickness of the silicon thin film.

The photoresist was removed. In order to have uniform conductivity throughout, a 10 nanometer nickel film was formed by sputtering, this was used as an electrode, and 300 micrometers of nickel was electroformed, and this was peeled off from the glass original plate to obtain a stamper. When the surface shape of the obtained stamper was measured, the width of the groove was 200 nanometers. Figure 8 shows specific grooves (12 in Figure 8) and pits (12 in Figure 8).
3) shows the cross-sectional shape. The depth of the groove is 45 nanometers, which corresponds to about half the thickness of the silicon film. The pit corresponds to the thickness of the silicon thin film, which is 80 nanometers.

(Example 2) A photoresist was applied to a 6-inch diameter silicon substrate to a thickness of 100 nanometers by spin coating, and fixed by baking. The silicon substrate on which the photoresist layer has been formed is placed on a laser cutting machine, and a laser beam with a wavelength of 442 nanometers is focused using an objective lens with a numerical aperture of 0.9, condensing it onto the photoresist at a pitch of 0.8 micrometers. Then, the laser was flashed periodically to perform a spiral exposure. The blinking period of the laser was set at a pitch of 0.5 micrometers on the rotating silicon substrate. Next, the exposed portions of this photoresist were developed. Next, the silicon substrate was etched by reactive ion etching to remove the photoresist.

A photoresist was again applied to a thickness of 100 nanometers on the silicon substrate, and exposed using a laser cutting machine. In this exposure process, continuous exposure was performed to form grooves between pits using the pits previously formed on the silicon substrate as guides. After developing the photoresist, etching was performed.

In order to provide good electrical conductivity to the whole, a 10 nanometer nickel film was formed by sputtering, this was used as an electrode, and 300 micrometers of nickel was electroformed, and this was peeled off to obtain a stamper. When the surface shape of the obtained stamper was measured, the pits were circular with a diameter of 200 nanometers. The depth was approximately 60 nanometers. In this case, the pit depth can be freely changed depending on the etching time. The subsequently formed grooves were approximately 150 nanometers wide and approximately 30 nanometers deep. Furthermore, silicon substrates are lightweight, have good surface properties, and do not warp, making them extremely easy to handle. Furthermore, unlike a silicon film on a glass original plate, the crystal orientation is aligned, so it has the advantage that etching can be performed uniformly.

(Example 3) A silicon oxide film was used as a film to be formed on a glass original plate. When the same experiment as in Example 1 was conducted, almost the same results were obtained. Further, the same results were obtained when the film was a silicon nitride film or an aluminum film.

(Example 4) A photoresist was applied to a silicon substrate having a diameter of 8 inches by a spin coating method to a thickness of 100 nanometers, and was fixed by baking. The silicon substrate on which the photoresist layer has been formed is placed on a laser cutting machine, and a laser beam with a wavelength of 442 nanometers is focused using an objective lens with a numerical aperture of 0.9, condensing it onto the photoresist at a pitch of 0.8 micrometers. Then, the laser was flashed periodically to perform a spiral exposure.

In the configuration shown in FIG. 7(b), on the optical path of the cutting laser, one side of the bottom surface of the cylinder having the shape shown in FIG. 7(b) is hollowed out into a conical shape, and the other side is hollowed out into a conical shape A protruding prism was inserted to create a gap with a width equivalent to 30% of the diameter of 1/2 the intensity of the beam center, and this beam was focused with an objective lens. In this case, the width of the main spot could be made 25% thinner than when nothing was done.

The blinking period of the laser was set at a pitch of 0.5 micrometers on the rotating silicon substrate. Next, the exposed portions of this photoresist were developed. Next, the silicon substrate was etched by reactive ion etching to remove the photoresist.

A photoresist was again applied to a thickness of 100 nanometers on the silicon substrate, and exposed using a laser cutting machine. In this exposure process, continuous exposure was performed to form grooves between pits using the pits previously formed on the silicon substrate as guides. After developing the photoresist, etching was performed.

In order to provide good electrical conductivity to the whole, a nickel film of 10 nanometers was formed by sputtering, and this was used as an electrode to electroform nickel to 300 micrometers, and this was peeled off to obtain a stamper. When the surface shape of the obtained stamper was measured, the pits were circular with a diameter of 200 nanometers. The depth was approximately 60 nanometers. In this case, the pit depth can be freely changed depending on the etching time. The subsequently formed grooves were approximately 150 nanometers wide and approximately 30 nanometers deep.

(Example 5) A silicon thin film of 60 nanometers was formed by sputtering on a glass original plate having a thickness of 10 mm and a diameter of 200 mm. A photoresist was applied onto this silicon thin film to a thickness of 100 nanometers by spin coating, and fixed by baking. The glass original plate on which the silicon thin film and photoresist layer have been formed is placed on a laser cutting machine, and a laser beam with a wavelength of 442 nanometers is focused by an objective lens with a numerical aperture of 0.9 and focused onto the photoresist. Exposure was performed in a spiral manner at a micrometer pitch. Next, the exposed portion of this photoresist was developed and removed, and then the silicon thin film was etched by plasma etching to remove the photoresist. In order to have uniform conductivity throughout, a 10 nanometer nickel film was formed by sputtering, this was used as an electrode, and 300 micrometers of nickel was electroformed, and this was peeled off from the glass original plate to obtain a stamper. When the surface shape of the obtained stamper was measured, the width of the groove was 400 nanometers. This width is approximately the same as the groove width formed using only conventional photoresist. A polycarbonate substrate is made from this stamper by injection molding, and this substrate is used to make a magneto-optical recording disk, and the narrow band S/N ratio (C/N) of the recorded signal is ratio)
When measured, it was found that the noise level was improved by 2 dB.

Although reactive ion etching was used in the present Examples except for Example 5, other dry etching methods may be used as long as they do not increase the etching width in accordance with the purpose of the present invention. can not use.

[0032]

As shown in the examples, by using the present invention, it is possible to manufacture a stamper with a fine pattern that cannot be obtained by the current mastering method. The width and length of the grooves and pits to be produced can be controlled not by the laser beam width for cutting, but by the thickness of the photoresist, the laser beam intensity, etc. Furthermore, according to the present invention, it is also possible to form pits or grooves with different depths within the same substrate. Furthermore, when the present invention is used, the edges of the grooves and pits are smoother than when only conventional photoresist is used, and the S/R of the optical recording medium manufactured using the obtained stamper is smoother. It also has the effect of improving the N ratio. Therefore, it can be seen that the present invention is effective even in conventional applications that do not require high-density patterns.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the first half of the method for manufacturing an optical recording medium of the present invention.

FIG. 2 is a schematic diagram showing the first half of the method for manufacturing an optical recording medium of the present invention.

FIG. 3 is a schematic diagram showing the latter half of the method for manufacturing an optical recording medium of the present invention.

FIG. 4 is an explanatory diagram showing a beam intensity distribution of a laser beam in a laser cutting machine.

FIG. 5 is a cross-sectional view showing an exposed area of a photoresist.

FIG. 6 is a cross-sectional view showing the relationship between an exposed area and an etched area of a photoresist.

FIG. 7 is a schematic cross-sectional view showing a method of inserting a mask and a prism in the laser path.

FIG. 8 is a cross-sectional view showing the surface shape of a stamper manufactured by the manufacturing method of the present invention.

[Explanation of symbols]

1　Glass original plate 2 Inorganic membrane 3 Photoresist 4 Exposure section 5 Etched part 6 Electroforming 7 Stamper 8 Silicon substrate 9 Objective lens 10 Mask 11 Prism 12 Cross section of groove 13 Cross section of pit

Claims (6)

[Claims] 1. Forming an inorganic film of metal, semiconductor, oxide, or nitride on a glass original plate, applying a photoresist on the inorganic film, and exposing the photoresist to a laser beam, The photoresist exposed by the laser beam is developed to remove the exposed portion, the inorganic film exposed by the removal of the exposed portion of the photoresist is etched, and then the photoresist is removed. , a first step of forming grooves or pits in the inorganic film, and applying a photoresist on the inorganic film that has undergone the first step to remove the grooves or pits formed in the first step. The grooves or pits formed in the first step are removed by performing the same exposure and development treatment as in the first step, and etching the inorganic film again while aligning the position of the exposure laser beam. After a second step of forming grooves or pits with different widths or depths, the grooves or pits are transferred to a metal plate by electroforming, and the metal plate is used as a mold,
A method for manufacturing an optical recording medium, comprising transferring the grooves or pits to plastic. 2. The manufacturing method according to claim 1, wherein the laser beam for exposing the photoresist is light having a distribution in which the intensity is highest at the center of the laser beam and decreases toward the periphery of the laser beam, and A method for manufacturing an optical recording medium, characterized in that the exposure width of the photoresist is wide on the side of the laser beam incident surface of the photoresist and narrow on the side of the surface in contact with the inorganic film. 3. The manufacturing method according to claim 1, wherein the intensity distribution within the laser beam has a substantially Gaussian distribution, and a mask disposed in the path of the laser beam;
Alternatively, the intensity distribution of the spot focused by the lens on the photoresist is made to have large side lobes and the width of the main spot is narrower than in the case where there is no mask or prism, using a prism. A method for manufacturing an optical recording medium. 4. Applying a photoresist on a silicon substrate, exposing the photoresist to a laser beam, developing the photoresist exposed to the laser beam to remove the exposed portion, and further removing the exposed portion of the photoresist. a first step of etching the silicon substrate exposed by removing the exposed portion of the resist, and then removing the photoresist to form a groove or pit in the silicon substrate; A photoresist is applied on the silicon substrate, and the same exposure and development processes as in the first step are performed while aligning the exposure laser beam using the grooves or pits formed in the first step. and a second step of etching the silicon substrate again to form grooves or pits having a width or depth different from the grooves or pits formed in the first step,
A method for manufacturing an optical recording medium, comprising transferring the grooves or pits onto a metal plate by electroforming, and further transferring the grooves or pits onto plastic using the metal plate as a mold. 5. The manufacturing method according to claim 3, wherein the laser beam for exposing the photoresist is light with a distribution in which the intensity is highest at the center of the laser beam and the intensity decreases toward the periphery of the laser beam, and 1. A method for manufacturing an optical recording medium, characterized in that the exposure width of the resist is wide on the side of the laser beam incident surface of the photoresist and narrow on the side of the photoresist in contact with the silicon substrate. 6. The manufacturing method according to claim 4, wherein the intensity distribution within the laser beam has a substantially Gaussian distribution, and a mask disposed in the path of the laser beam;
Alternatively, the intensity distribution of the spot focused by the lens on the photoresist is made to have large side lobes and the width of the main spot is narrower than in the case where there is no mask or prism, using a prism. A method for manufacturing an optical recording medium.