JP2003006943A - Method of manufacturing optical master disk and optical master disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical master disk on which permit the stable formation of pits of different thicknesses and continuous grooves within the same disk. SOLUTION: In the method of manufacturing the optical master disk 9 having recessed parts of two kinds of depths, the deep recessed parts 7 and the shallow recessed parts 8 on a substrate 1 by using a photoresist, the sensitivity curve of the photoresist applied to the substrate has the characteristics that the straight line gradient of exposure energies Eo to Eth and the straight line gradient of exposure energies Eth to Ehalf are substantially different and the straight line gradient of the exposure energies Eo to Ehalf is less steeper than the exposure energies Eth to Ehalf when the exposure energy beginning the reduction of the film thickness after the development by increasing of the exposure energy is defined as Eo and the lowest exposure energy at which the film thickness is zero is defined as Eth and the certain exposure energy between the exposure energies Eo to Ehalf as Ehalf and that the substrate is irradiated with the exposure energy above Eth in the regions the deep recessed part are ought to be formed and the substrate is irradiated with the exposure energies of Eo to Ehalf in the regions where the shallow recessed parts are ought to be formed, by which the recessed parts of two kinds of the depths, the deep recessed parts and the shallow recessed parts are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical disk master and an optical disk master, and more particularly to an optical disk having two kinds of areas, a pit area and a continuous groove area, each having different depth as a recess on the same master. Regarding the master.

[0002]

2. Description of the Related Art Generally, an optical disc has a large recording capacity and can be recorded and reproduced in a non-contact manner.
ROM-type disc such as DVD-video or C
Write-once discs such as D-R and DVD-R, and CD
-Widely used for rewritable discs such as RW, DVD-RAM and DVD-RW. Here, a general manufacturing method for forming an optical disk will be described. Figure 5
FIG. 3 is a diagram for explaining the outline of a general manufacturing process of an optical disc. First, a photoresist layer 11 is formed on a substrate 10 made of glass or the like whose surface is polished and washed by spin coating or the like.
To form a blank master BL (FIG. 5).
(A)).

Next, a beam 12 of Ar, Kr, He-Cd laser or the like is condensed by an objective lens 13, and a minute spot is irradiated on the photoresist layer 11 formed on the substrate 10. At this time, the laser beam 12 is turned on and off while rotating the glass substrate 10 and moving at a constant speed.
By doing so, or by continuously irradiating the beam 12, the latent image 14 of pits and grooves is formed in a spiral shape (FIG. 5B). Then, the photoresist layer 11 is subjected to a developing treatment with an alkaline solution to remove the portion of the latent image 14 so that an optical disc master D1 having pit and groove patterns 15 is formed (FIG. 5). (C)). A conductive film 1 of nickel or the like is formed on the surface of the optical disc master D1 manufactured as described above by a method such as sputtering or electroless plating.
6 is formed (FIG. 5D).

Next, by using a plating method in which the conductive film 16 is used as a cathode and nickel is arranged on the anode side to conduct electricity in a nickel sulfamate solution,
Nickel 17 is deposited on the optical disc master D1 (FIG. 5 (e)). Then, the deposited nickel 17 is peeled off from the optical disc master D1 to obtain a metal master having a signal pattern formed on the surface thereof, that is, the stamper 1
8 is produced (FIG. 5 (f)). The above is the outline of the master disk manufacturing process, and the stamper 18 is used to mass-produce optical disks in the disk manufacturing process. The stamper 18 is incorporated into a molding die installed in a molding machine after being subjected to post-processing such as inner / outer diameter processing or back surface polishing. As a molding method, a synthetic resin such as an acrylic resin having a light-transmitting property or a polycarbonate resin is used as a material,
Molding using the stamper 18 as a female mold is performed by a compression (compression molding) method, an injection (injection molding) method, a photopolymer (2P) method, or the like (FIG. 5G). Then, the optical disk substrate 19 is manufactured by separating this male mold.

In the next film forming step, a concave-convex pattern corresponding to the concave-convex pattern of the stamper 18 is transferred, and a concave portion corresponding to a pit convex portion of the stamper 18 based on an information signal,
That is, the reflection layer 21 is formed by forming a film of aluminum or the like on one main surface side of the optical disc substrate 19 on which the pits 20 are formed. As a film forming method, a vapor deposition method or a sputtering method is used (FIG. 5 (h)). Next, in order to protect the reflective layer 21, an acrylic ultraviolet curable resin or the like is applied and cured by a spray method, a roll coating method, a spin coating method or the like to form a protective layer 22 (FIG. 5).
(I)). Finally, the label portion 23 is formed on the protective film 22 with ultraviolet curable ink or the like to complete the optical disc D3 (FIG. 5 (j)).

By the way, in recent years, as an application of the write-once and rewritable discs, an optical disc in which a reproduction-only area used only for reproducing information and a recordable area in which a user can record information are proposed has been proposed and commercialized. There is. For example,
An example is a disk in which pits are recorded on the inner peripheral portion to make a read-only area and a tracking guide groove is recorded on the outer peripheral portion to make a recordable area. The information recorded in the reproduction-only area is, for example, the address information of the recording groove, the information for indicating the type of the recording disc or the manufacturer, and recently, for preventing illegal duplication. It may also be disk management information.

[0007]

By the way, in an optical disc having a pit, a signal is usually detected by utilizing a phase difference between a pit portion and a non-pit portion, so that the pit depth is λ / (4 · n). (Λ: reproduction laser wavelength, n: refractive index of substrate). On the other hand, in an optical disc having a groove, the groove is present as a guide groove for the optical head to accurately follow the groove at the time of recording, and after information is recorded, tracking is performed by relying on the recorded mark row. Therefore, the depth of the groove is set so that tracking can be easily performed before the recording and the recording mark is not affected after the recording. In the case of the land / groove recording method, the depth is set so that the influence of the signal from the adjacent groove is reduced when the mark recorded on the land is detected. Generally, the depth is set to a value near λ / (6 · n) or less.

As described above, since the pits and the grooves have optimum depths for each of them, in the case of an optical disc in which the pits and the grooves are mixed, the depths of the pits and the grooves need not be changed. Don't However, in an optical disc manufactured through the above-described normal optical disc master manufacturing process, the depths of the pits and the grooves are naturally the same. In a DVD-RAM commercialized in recent years, the pit depth (= groove depth) is set so that pits, lands, and grooves are optically balanced. Also,
In the DVD-RW disc, the groove depth is extremely shallow because the groove depth does not affect the signal output of the recording mark as much as possible.
(10 · n) to λ / (18 · n) is selected. If you want to create a pit-only playback area here,
The signal from the pit cannot obtain a sufficient phase difference.

As described above, in order to achieve both the reproduction signal quality in the reproduction-only area and that in the recordable area, it is necessary to change the depths of the pits and the grooves in the same disk. Is required to improve. In order to solve the above problems, an optical disk master produced through a normal process is etched to form irregularities on this glass surface, and then a resist is applied again on the glass surface and cutting is performed to form grooves and pits. A method of changing the depth has been proposed (for example, JP-A-9-35334). However, in this method, the same step is performed twice, and an etching step is added, so that there is a problem of increased cost. In addition, after the first cutting, the optical disk master is removed from the turntable, and after etching, it is reattached and cut. There is also a problem that it is very difficult to continuously form a joint with the formed groove (or pit), and the optical head cannot follow when reproducing.

When the photoresist is applied, a low-sensitivity photoresist is formed in the lower layer and a high-sensitivity photoresist is formed in the upper layer, and only the upper-layer high-sensitivity resist is exposed to light and the lower-layer low sensitivity is exposed. A method has also been proposed in which the amount of exposure to the resist is used properly (Japanese Patent Laid-Open No. 8-451).
No. 16, JP-A-8-180468, and JP-A-8-180468.
-203131, JP-A-8-221808, JP-A-8-335333, and JP-A-9-723.
No. 5, etc.). Although this method requires only one cutting, it requires double coating in the photoresist coating step, and in some cases even an intermediate layer is required, and there are problems that the number of steps is increased and the steps are complicated.

Further, as another method, there has been proposed a method of exposing a region requiring a depth with a high exposure amount and a shallow region with a low exposure amount during cutting (JP-A-6-
36287, JP-A-9-102142, JP-A-9-251669, etc.). However, in this method, variations in the groove depth and width of the region subjected to low exposure irradiation pose a problem. In other words, exposure with an exposure amount that exposes halfway in the thickness direction of the photoresist means exposure in a region that is extremely sensitive to variations in the exposure amount in the sensitivity characteristics of the photoresist. Becomes
Even a slight change in the exposure dose causes a great change in depth and thickness.

Further, as another method, a method is also proposed in which the groove is made shallow by first irradiating an exposure amount enough to form a deep groove or pit, and then exposing the entire surface again only in an area where the depth is to be made shallow. (JP-A-8
No. 249728, JP-A No. 11-39729, etc.). However, this method has problems that the apparatus itself is complicated, for example, a light source for re-exposure is required, and it is difficult to control the exposure amount of the second exposure. The present invention has been made in view of the above problems and was devised in order to effectively solve them. The purpose is to stably form pits and continuous grooves having different depths in the same disk. An object of the present invention is to provide a method of manufacturing an optical disc master and an optical disc master.

[0013]

As a result of intensive studies to solve the above-mentioned problems, the present inventor found that the sensitivity characteristic of a photoresist used as a recording material was added to obtain the same characteristics. The present invention has been achieved by finding a method for easily forming recesses having different depths in a plane. The invention defined in claim 1 is a method of manufacturing an optical disk master having a recess having two kinds of depths, a deep recess and a shallow recess, on a substrate using a photoresist, and the sensitivity of the photoresist applied to the substrate. The curve shows that the exposure amount at which the film thickness after development starts to decrease due to the increase of the exposure amount is E _o , the minimum exposure amount at which the film thickness becomes zero is E _th , and the exposure amount E.
_When the exposure amount between _{o and} E _th is E _half , the exposure amount E _o
Unlike linear gradient to E _half and a linear gradient of exposure E _th to E _half is substantially linear gradient of exposure E _o to E _half is slower than a linear gradient of exposure E _th to E _half In the region where the deep recess is to be formed, an exposure amount of E _th or more is applied, and in the region where the shallow recess is to be formed, an exposure amount of E _{o to} E _half is applied so that the deep recess and the shallow recess are formed. A method for manufacturing an optical disc master is characterized in that recesses having two types of depths are formed.

In this case, for example, the film thickness of the photoresist is 50 to 200 nm as defined in claim 2. The invention defined in claim 3 is an optical disk master manufactured by using the method for manufacturing an optical disk master described above.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method of manufacturing an optical disc master and an optical disc master of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a process diagram showing a method for manufacturing an optical disk master according to the present invention, FIG. 2 is a graph showing sensitivity characteristics of a positive photoresist used in the present invention, and FIG. 3 is a sensitivity characteristic of a positive photoresist used in the present invention. 4 is a graph showing the baking temperature dependency of FIG. 4, and FIG. 4 is a graph showing the sensitivity characteristics of the positive photoresist conventionally used in the method for manufacturing an optical disk master.

First, as shown in FIG. 1C, an optical disk master 9 of the present invention is provided with a photoresist film 2 which has been exposed and developed on a substrate 1 made of, for example, a glass plate. Then, for example, a pit 7 is formed as a deep recess and a continuous groove 8 is formed as a shallow recess in the photoresist film 2. As described above, since the photoresist having the special sensitivity characteristic is used in the present invention to form the recesses 7 and 8 having different depths, the characteristic will be described in comparison with the sensitivity characteristic of the conventional photoresist. . First, as described above, FIG. 4 shows the sensitivity characteristics of a positive photoresist which has been generally used in the past for manufacturing an optical disc master. In this figure, the exposure amount at which the film thickness of the positive photoresist after development starts to decrease due to the increase in the exposure amount is E _o, and the minimum exposure amount at which the film thickness becomes zero is E _th . That is, it is shown that by irradiating with an exposure amount of E _th or more, a recessed portion that has penetrated to the bottom of the photoresist film is formed, and with an exposure amount of E _o or less, no recessed portion is formed. The linear gradient on this sensitivity curve is the γ value (= tan θ).

Forming the shallow concave portion by applying the above-mentioned low-exposure dose irradiation means that the low-exposure dose is applied from E _{o to} E _th . Therefore, in a photoresist having such characteristics, since the film thickness of the photoresist changes very sensitively with respect to the change of the exposure amount, variations in depth and groove width become large, which is preferable. Absent. On the other hand, as shown in FIG. 2, the sensitivity characteristics of the positive photoresist 2 used in the present invention are such that the film thickness gradually decreases up to a certain exposure amount E _half, and when the exposure amount becomes E _half or more, the film is formed. The thickness decreases sharply. That is, the feature is that the γ value of the linear gradient greatly changes at the exposure amount E _half (E _{o to} E _half = γ1, E _{half to} E _th = γ2). Therefore, when the exposure amount is E _half or less, the amount of change in film thickness with respect to the change in exposure amount is small. Therefore, when a shallow recess is formed, if an exposure amount of E _{o to} E _half is applied, a groove is formed in a region with a large exposure amount margin. Can be formed. On the other hand, when forming a deep recess, it is sufficient to irradiate with an exposure amount equal to or more than E _{th as in the} conventional case.

Now, the positive photoresist having such sensitivity characteristics will be specifically described. As a result of extensive studies on a photoresist for realizing the sensitivity characteristic as shown in FIG. 2 in a single layer, it was found that it can be realized by using a conventionally known lift-off photoresist. The lift-off photoresist is a resist originally used in a semiconductor process, and details thereof are disclosed in JP-A-8-69111 and JP-A-10-142783. Normally, in the semiconductor process, the resist film thickness is 1
The resist film thickness is 50 to 2
It was found that a unique sensitivity characteristic can be obtained by using it in an optical disk process in the range of 00 nm. Although this mechanism is not clearly known, it can be considered as follows.

In the case of the optical disc manufacturing process, the resist is applied in a very thin film thickness of 0.2 μm or less, so that the dilution ratio of the resist solution is larger than that in the semiconductor process, and as a result, the spin coating after spin coating is performed. The ratio of the residual solvent contained in the resist film also increases. Although this residual solvent is removed by baking, the concentration gradient of the photosensitizer component is not formed by the volatilization of the solvent component and the diffusion of the photosensitizer component upward in the film at the same time. It is thought that. It is considered that this concentration gradient is formed also in the semiconductor process, but in the manufacturing process of the optical disc, since the solvent component is large, the degree of freedom of the photosensitizer itself increases, so that the diffusion becomes easy and a sharper concentration gradient is formed. It is thought to be done. When such a concentration gradient of the photosensitizer is formed in the film, the upper layer and the lower layer have different sensitivities, so that the two-step sensitivity characteristic as shown in FIG. 2 can be realized. Hereinafter, the method for producing an optical disk master according to the present invention will be described more specifically, but the present invention is not limited to the following examples unless it exceeds the gist.

First, as shown in FIG. 1A, a disc-shaped glass substrate 1 having a diameter of 200 mm and a thickness of 10 mm, which has been precisely polished as a substrate, is exposed to vapor of hexamethyldisilazane for 3 minutes. Adhesion is imparted to the surface of the glass substrate 1. Next, a lift-off positive photoresist (LOR-P003, manufactured by Tokyo Ohka Kogyo Co., Ltd.) diluted with a solvent (2-heptanone) is uniformly applied by spin coating. Finally, by baking this on a hot plate at 120 ° C for 10 minutes, a film thickness of 100 nm is obtained.
To obtain a photoresist film 2. The sensitivity characteristics of the photoresist film 2 thus obtained are shown in FIG. As described above, it can be seen that the slope γ changes greatly at the exposure amount E _half as a boundary. The sensitivity characteristic was determined by multi-step exposure using a contact exposure machine by separately preparing a substrate.

Next, as shown in FIG. 1B, a krypton laser beam 3 having a wavelength of 351 nm is condensed by an objective lens 4 in order to record a pit and a continuous groove in the same plane,
This was irradiated onto the photoresist film 2 and exposed. At this time, the exposure amount by the laser power was set to be E _th or more in the area 5 where the pits are formed, and E _o or more and E _half or less (the range of E _{o to} E _half ) in the area 6 where the continuous groove is formed. Then, the entire glass substrate 1 was developed with a 0.7% tetramethylammonium hydroxide aqueous solution for 60 seconds to dissolve the exposed portion to obtain an optical disc master 9 having pits 7 and continuous grooves 8 (see FIG. 1 ( See c)). As a comparative example, a conventional positive photoresist (THMR-iP3100, manufactured by Tokyo Ohka Kogyo Co., Ltd., solvent: ethyl lactate + butyl acetate mixed solvent) was used to obtain an optical disk master in the same manner.

After that, a stamper is manufactured by using each of the optical disk masters obtained as described above through the same process as described above with reference to FIG. 5, and an optical disk substrate is formed by an injection molding method using a polycarbonate resin. It was made.
With respect to the depth of the continuous groove of each optical disk substrate thus obtained, the groove depth was measured at 16 points in the entire circumference of the disk by an atomic force microscope, and the maximum value and the minimum value thereof were calculated. As a result, when the normal type positive photoresist of the comparative example is used, the maximum value is 28.3 nm and the minimum value is 18.
It was 3 nm and the difference was 10 nm. On the other hand, when the lift-off positive photoresist of the present invention is used, the maximum value is 24.8 nm and the minimum value is 22.3n.
m, and the difference was 2.5 nm.

That is, in the case of the present invention, the variation in the depth of the shallow recess 8 which is a continuous groove is reduced to 1/4 (= 10 / 2.5) as compared with the comparative example of the conventional example. It turned out that it was a good characteristic. Regarding the baking conditions after the resist application, 120 in the above embodiment.
Although the temperature is set to 10 ° C. for 10 minutes, the temperature is not limited to this, and can be changed according to the thickness of the glass substrate, the desired groove depth, and the like. FIG. 3 shows the relationship between the baking temperature and the sensitivity characteristic of the photoresist used in the present invention. Here, the baking temperatures are 80 ° C. and 100 ° C.
And 120 ° C. are shown. This shows that the sensitivity and the position of the exposure amount E _half are changed depending on the baking temperature. It is presumed that this is because the baking temperature causes a difference in the diffusivity of the photosensitizer, resulting in a difference in the concentration gradient. Therefore, the baking temperature condition can be changed depending on the target groove depth.
Further, although a positive type photoresist is used in this embodiment, the photoresist is not limited to this, and a negative type photoresist can also be used. In this case, the relationship between the exposure dose and the film thickness shown in FIG.

[0024]

As described above, according to the optical disc master manufacturing method and the optical disc master of the present invention, the following excellent operational effects can be exhibited. It is possible to stably form pits and continuous grooves with different depths in the same disc without changing the conventional process.
It is possible to improve the yield in the manufacturing process of the optical disc in which the read-only area and the recordable area are mixed and to stabilize the recording / reproducing characteristics.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for manufacturing an optical disc master according to the present invention.

FIG. 2 is a graph showing the sensitivity characteristics of the positive photoresist used in the present invention.

FIG. 3 is a graph showing the baking temperature dependence of the sensitivity characteristics of the positive photoresist used in the present invention.

FIG. 4 is a graph showing the sensitivity characteristics of a positive photoresist which has been conventionally generally used for manufacturing an optical disc master.

FIG. 5 is a process drawing showing a general method for manufacturing an optical disc master.

[Explanation of symbols]

1 ... Substrate, 2 ... Photoresist film, 7 ... Deep recess, 8 ...
Shallow recess, 9 ... Optical disc substrate.

Claims (3)

[Claims] 1. A method of manufacturing an optical disc master having a photoresist and a depression having two kinds of depths, a deep depression and a shallow depression, on a substrate, wherein a sensitivity curve of the photoresist applied to the substrate is:
The exposure amount at which the film thickness after development starts to decrease due to the increase in the exposure amount is E _o , the minimum exposure amount at which the film thickness becomes zero is E _th , and the exposure amount between exposure amounts E _{o to} E _th is E _half. , The linear gradient of the exposure amounts E _{o to} E _{half and} the linear gradient of the exposure amounts E _{th to} E _half are substantially different, and the linear gradient of the exposure amounts E _{o to} E _half is equal to the exposure amounts E _{th to} E _half. It has the characteristic of being slower than linear gradient of the deep in the area to be formed the recess is irradiated with the exposure amount of more than E _th, the E _o to E in the region for forming the shallow recess
_A method for manufacturing an optical disk master, characterized in that a concave portion having two kinds of depths, that is, a deep concave portion and a shallow concave portion is formed by irradiating a _half exposure amount. 2. The photoresist has a film thickness of 50 to 20.
The method for producing an optical disk master according to claim 1, wherein the optical disk master is 0 nm. 3. An optical disk master manufactured by the method for manufacturing an optical disk master according to claim 1.