JP2001110096A - Method of manufacturing information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the pit finer than heretofore and to make the pit pattern density higher. SOLUTION: In forming pit string patterns, a photosensitive layer is exposed by a first light spot which exposes the pit patterns and a second light spot which exposes grooves partly overlapping the side parts of the pit patterns apart a distance of approximately n/2 (where n is an integer) of the track pitch in the radial direction from the first light spot. When the groove width in the sectional shape of a trapezoidal shape in the radial direction of the grooves is given as the mean value of the upper base and lower base of the trapezoidal shape at this time, its value Wg is so set as to attain T.Px0.50<=Wg<=T.P×0.60 with respect to a track pitch T.P. When a substrate is directly etched, the width Wa at the boundary between the photosensitive layer and a supporting body corresponding to the grooves prior to etching is so set as to attain (T.P×0.50)-45 nm<=Wa<=(T.P×0.60)+45 nm with respect to the track pitch T.P. In either case, the surface of the photosensitive layer is preferably subjected to a hardly solubilizing treatment by immersing the surface into a developer prior to the exposure stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an information recording medium such as an optical disk, a magneto-optical disk, and a phase change optical disk, and more particularly to a technique of manufacturing a mastering master.

[0002]

2. Description of the Related Art Conventionally, in this type of information recording medium (for example, an optical disk 101), as shown in FIG. 17, in a signal recording area 102, one surface 104 of an optically transparent plastic disk substrate 103 is provided. The continuous groove-like groove 105 or the pit row 108 is provided spirally at a predetermined track pitch p (0.7 to 1.6 μm) for each track.

For example, as for a read-only optical disk (ROM) having a pit row structure, as shown in FIG. 18, many use a row of pits 108 on a surface 104 as a recording area and a tracking diffraction grating. ing. A light reflection layer (not shown) is formed on the surface 104 on which the rows of the pits 108 are provided. As for a recordable optical disk of a phase change type or a magneto-optical type which mainly has a groove structure, as shown in FIG. (For example, groove 10
5) is used as a tracking light reflection area. On the surface 104 on which the groove 105 is provided, a phase change film, or a magnetic film and a light reflection layer (both not shown) are formed. However, even in these recordable discs, ancillary signals such as disc-specific information or addresses are usually inserted by the pit train 108.

Further, there is a partial ROM disk that shares a ROM area and a recordable area on one recording surface.

While rotating these optical discs, a laser beam is irradiated from an optical pickup (not shown) onto a surface 107 of the substrate 103 opposite to the one surface 104.
In the future, irradiation with laser light from the surface 104 side is also considered.

[0006] In a read-only optical disk, information reading and tracking are performed by detecting reflected / diffracted light from a surface 104 provided with a row of pits 108 with respect to light irradiated to a surface 107. In a recordable optical disk, information is written on, for example, a recording layer on the land 106 by irradiation light, or information written on the recording layer is read by reflected light. Further, tracking is performed, for example, by detecting reflected light from the groove 105 so that a laser beam for recording or reproduction is always irradiated on a predetermined track.

As described above, since the unevenness of the surface of the optical disk substrate 103 affects the performance as an information recording medium, it is required to manufacture the substrate 103 with high precision.

A method for manufacturing the substrate 103, which is an actual manufacturing process at present, will be described with reference to FIG.

First, on a glass master (or glass substrate) 123 whose surface has been sufficiently polished and washed, a photoresist 120 which becomes alkali-soluble by exposure treatment is applied to a thickness of about 0.1 μm.

Next, a recording laser beam 131 is condensed on the surface of the photoresist 120 by an objective lens 132 and is exposed. At this time, while rotating the glass master disk 123,
By sending the laser beam 131 turned on / off in response to the recording signal in the radial direction at an equal distance per rotation, a latent image 133 in a row of pits 128 is formed in the photoresist 120 in a spiral at each track pitch.

At this time, if the laser beam irradiation is performed continuously (DC irradiation), the latent image
33 occurs.

Next, the master is developed with an alkaline developer to expose the exposed portion (ie, the photoresist 120).
). Thus, in the read-only optical disk, a continuous row of pits 128 is repeatedly formed in the radial direction. In a recordable optical disk, a continuous groove 125 called a groove and a convex part 126 called a land left between the continuous grooves are alternately formed in the photoresist 120 in the radial direction.

Next, Ni stamping is performed on the glass master disk 123 to produce a stamper 134 in which a continuous pit row or continuous groove of the photoresist 120 is transferred. Next, the uneven surface of the stamper 134 is transferred to a plastic material as a substrate material of the optical disk by an injection molding method or the like, and the rows of pits 108 as shown in FIG. 18 or the grooves 105 and lands 106 as shown in FIG. Each is formed and a replica (substrate 103) is manufactured.

As for a read-only optical disk,
A reflective film and a protective film are formed on the uneven surface of the substrate 103 having the pits 108. As for the recordable optical disk, the groove 1 of the substrate 103 is formed after the replica is made.
A recording film, a reflection film, and the like are formed on the uneven surface on which the reference numeral 05 is formed.

[0015]

In recent years, DVD ROM disks having a recording density of about five times that of conventional CDs have been commercialized, and at the research and development stage, the density of DVD disks has been doubled. Optical discs have already been announced. Such high density is the main theme of optical disc development.

Therefore, there is a demand for a mastering technique capable of forming finer pits.

The present invention has been proposed in view of the above-mentioned conventional situation, and is intended to manufacture an information recording medium capable of further reducing the size of pits and improving the pit pattern density. The aim is to provide a method.

[0018]

According to the present invention, a new process is devised by changing or adding to the above-described substrate manufacturing process for the purpose of improving the pit pattern density in a ROM disk.

That is, the present invention provides a step of forming a photosensitive layer on a support, a step of exposing a predetermined area of the photosensitive layer,
Developing after exposure, forming a concavo-convex pattern corresponding to the pit row pattern on the photosensitive layer, and forming, on the substrate, concavities and convexities involved in recording and / or reproducing information based on the concavo-convex pattern. In the method for manufacturing an information recording medium, a first light spot for exposing a pit pattern and the first light spot are approximately n / 2 of a track pitch in a radial direction (where n is an integer). And exposing the photosensitive layer with a second light spot that exposes a groove that partially overlaps the side portion of the pit pattern at a distance of, and, in a trapezoidal cross-sectional shape in the radial direction of the groove, the groove width is reduced. When given as an average value of the upper and lower bases of the trapezoid, the value Wg is the track pitch T. For T.P. P × 0.50 ≦ Wg ≦ T. It is characterized in that it is set to be P × 0.60.

The present invention also provides a step of forming a photosensitive layer on a support, a step of exposing a predetermined area of the photosensitive layer, and a step of developing after exposure to form a concavo-convex pattern corresponding to the pit row pattern on the photosensitive layer. A method of manufacturing an information recording medium, comprising: forming a concave and convex portion relating to recording and / or reproduction of information on a base on the basis of the concave / convex pattern; The light spot and the first light spot are exposed to a groove that partially overlaps the side portion of the pit pattern at a distance of about n / 2 (where n is an integer) of a track pitch in a radial direction. The step of exposing the photosensitive layer with the second light spot and the step of forming the irregularities directly on the support by etching using the photosensitive layer having the irregularities formed by the developing step as a mask and removing the remaining resist. To have a step, the track pitch T. The width Wa at the interface between the photosensitive layer and the support that corresponds to the groove before the etching For P, (TP × 0.50) −45 nm ≦ Wa ≦ (TP ××
0.60) +45 nm.

As a method of increasing the recording density of a read-only optical disk having a pit pattern, a side portion of a pit row is scraped with a groove to be exposed by another spot when a pit pattern is exposed on a mastering master. Thus, a two-beam exposure method for forming land pits narrower than the conventional one can be considered. This seems to be a very practical and promising method at present, as miniaturization of the exposure spot diameter has become difficult.

However, when this exposure method is used, the pits can be miniaturized, but the reproduction signal characteristics are hardly improved.

In the present invention, the groove design and the resist exposure conditions are optimized, whereby not only miniaturization of the pits but also the reproduction signal characteristics are greatly improved.

Also, by introducing a “pre-development process” in which a photoresist is immersed in a developing solution before exposure to form a hardly soluble layer on the resist surface, land pits that are unstable compared to normal pits are obtained. Since the boundary line of the bottom surface is formed clearly and stably, and the pits themselves are formed finer, the reproduction signal characteristics are improved and the density is increased.

Furthermore, since land pits are usually inverted from the pits and irregularities, it is very difficult to injection mold a plastic substrate from a master stamper obtained by a normal process. By using a mother stamper obtained by reversing the irregularities obtained by a single Ni plating transfer process, it is possible to obtain the same transferability of the injection molding as in the past.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an information recording medium to which the present invention is applied will be described in detail with reference to the drawings.

The process according to the present invention is first characterized by a pit exposure method. Therefore, the exposure step will be described in detail below.

First, a general configuration of an exposure apparatus (hereinafter referred to as a cutting machine) and an optical system will be described below.

As shown in FIGS. 1 and 2, the cutting machine mainly comprises (1) a recording laser beam 1 and (2) a recording light intensity control system 2: which removes the instability of the output of the light source, and In order to control the recording light intensity, a servo system using an electro-optic crystal element (EO) 21 is inserted. Specifically, a part of the output of the light source is guided to the photodetector 23 via the beam splitter 22, the output from the photodetector 23 is compared with a reference voltage, and the recording light power control circuit 23 feeds it back to the EO 21 to output the recording light. Control so that the intensity is constant. (3) Modulating section 3: a modulator 31 is formed in the optical system of the exposure apparatus in order to form a pit having a length corresponding to the electric recording signal.
To convert the recording signal voltage level into light intensity (for example, when the recording signal level is made up of two values of “1” and “0”, it is modulated to light on and off). Modulator 31
Is required to have a performance that can be used in a band of several tens of MHz, and an EOM (electro-optic crystal element modulator) or AOM (acousto-optic crystal element modulator) is usually used. Before and after the modulator 31, a lens L1 and a lens L2 are arranged. (4) Beam expander 4: an optical system for expanding the beam diameter of the recording light. Here, the convex lens L3 and the convex lens L
4, and the recording light is guided here by the beam splitter 42. The diameter of the focused spot is adjusted by the magnification of these convex lenses L3 and L4. (5) Objective lens 5 (6) Turntable 7 for holding and rotating glass master 6 (7) Mechanism 7 for moving glass master 6 and objective lens 5 perpendicular to the tangential direction of rotation (8) Object lens 5 and exposure Servo system 8 for keeping the distance of the surface constant at all times: Normally, a focusing laser 10 having a wavelength to which the photoresist 9 is not exposed is separately used. Composed of

When the recording signal level "1" is input to the modulator 31, the recording light passes through the modulator 31, the beam diameter is expanded by the expander 4, and then the objective lens 5
Is focused on the glass master 6 by the photoresist 9
Is exposed. When the recording signal level is "0", the recording light is not supplied to the subsequent optical system, so that the photoresist 9 is not exposed.

Since the glass master 6 is rotating, it has a relative degree V with respect to the spot. When a recording signal of level “1” is applied to the modulator 31 during the time T, the spot moves on the photoresist 9. Exposure is performed at a distance of L = V × T, and a pit having a length L is formed by development.

Further, by rotating the recording light in the radial direction at equal distances per rotation while rotating the glass master 6, latent images of pits or grooves are formed in a spiral shape at a fixed track pitch.

In the mastering step, an exposure step,
In particular, the recording spot diameter most directly determines the upper limit of the recording density of the optical disc.

The exposure spot diameter φ is the minimum φ = 1.22 × λ / NA at the diffraction limit from the recording light wavelength λ and the numerical aperture NA of the objective lens (Equation 1). Obviously, the smaller this is, the finer pits can be formed and the recording density can be improved.

From the above equation (1), there are two methods for reducing the exposure spot diameter φ: (1) shorten the recording light wavelength λ and (2) increase the numerical aperture NA of the objective lens.

However, the objective lens NA is already 0.90
0.95, which is generally used near the theoretical maximum value (NA <1.0). Regarding the recording wavelength, the use of ultraviolet (UV) light around λ = 350 nm has begun to be put into practical use, but shorter λ = 200 nm.
At present, there are many problems regarding the use of the deep UV region on the order of nanometers, such as the necessity of drastically changing conventional processes such as photoresists, difficulty in securing optical components, and harm to human bodies. Further, when the wavelength becomes shorter, a light source itself having both output and stability required for cutting cannot be found.

For the above reasons, it is difficult to obtain a smaller exposure spot diameter, and there is a need for a technique for forming finer pits by other methods. Even if the spot diameter becomes smaller in the future, it is always necessary to obtain the maximum recording density within a possible range by using the spot diameter, and such a technique is important anyway.

In view of the above circumstances, the applicant of the present invention has already proposed an exposure method that enables formation of a finer pattern with the current spot diameter.

Since the exposure method of the new mastering process of the present invention employs this, it will be described below.

Conventionally, as shown in FIG. 3, it is common knowledge that only one exposure spot A is used, and that the pit P is formed by exposing the exposed spot A and removing the resist by development to form a concave portion. Was.

On the other hand, in the above invention, FIG.
As shown in the figure, using two exposure spots A and B, 1
One spot A exposes a pit P as usual, and another spot B exposes a groove G so as to fill the middle of an adjacent track.

As a result, the convex land portion which is not exposed from either of the two recording spots and remains after development is regarded as a new pit LP. (Hereinafter referred to as land pits.) Land pits formed by this method are smaller in width than conventional pits, and the density in the radial direction can be improved. The minimum width Wp-min of the normal pit formed using one exposure spot is limited by the spot diameter, but the width W1 of the land pit is Wg, the width of the groove exposed by the side spot, and T.p. P, W1 = T. Since P-Wg, Wg
To T. By widening to a point close to P, it can be made considerably thinner regardless of the track pitch. At least W1 is less than Wp-min.

For example, recording wavelength λ = 35 for cutting
In the case of 1 nm and NA = 0.90, according to experiments, Wp-m
in = 0.15 μm, whereas T. in. P =
W1 at 0.50 μm is T. P-Wg = 0.11 μ
m (resist coating thickness d = 50 nm at this time).

This makes it possible to manufacture a higher density ROM disk with a narrower track pitch than in the prior art.

The cutting machine optical system for realizing such an exposure method will now be described.

At the time of cutting, so-called two-beam cutting using two exposure spots has been conventionally performed, and is actually used in, for example, an ISO standard MO in which address pits are inserted in the middle of adjacent groove rows.

FIG. 5 schematically shows a two-beam optical system. In FIG. 5, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted.

In the two-beam optical system, another channel (Ch-B) is newly opened in addition to the conventional channel (Ch-A).

First, by setting the transmittance of the Ch-A beam splitter 22A immediately after the EO 21 to about 50%, the Ch-A and the beam splitter 22B make the Ch-B beam splitter 22B.
Are made substantially equal in light amount. Alternatively, the transmittance may be arbitrarily selected according to the required light amount for each channel.

Ch-B may be the same optical system as Ch-A with respect to the modulator. Ch-A includes a modulator 31A, a lens L1A, a lens L2A, and a beam splitter 42A. Ch-B includes the modulator 31B and the lens L1.
B, a lens L2B, and a beam splitter 42B.

By using different modulators for each channel, it is possible to record different signals completely independently. For example, it is possible to simultaneously expose grooves in Ch-A and pits in Ch-B.

The beams of both channels are supplied to a polarizing beam splitter (PBS) 11 before the beam expander.
Join again at. That is, the Ch-A beam is guided to the PBS 11 via the half-wave plate 12, and the Ch-B beam is guided to the PBS 11 via the beam splitter 13, where they are combined.

The laser light is emitted in the state of linearly polarized light. As a result, before the PBS 11, the same channel has linearly polarized light in the same direction. The PBS 11 transmits 100% of linearly polarized light in a certain direction, and transmits linearly polarized light in a vertical direction by 1%.
Since the element reflects 00%, in order to utilize the light quantity of both channels to the maximum, the half-wave plate may rotate the linearly polarized light of one channel by 90 degrees. FIG. 5 shows a case where Ch-B reflects 100% and Ch-A rotated 90 degrees in the polarization direction by the half-wave plate transmits 100%.

In general, a half-wave plate has a direction of linearly polarized light which is defined by a polarization direction and a certain direction (crystal axis direction) in the plane of the wave plate.
Since the element rotates by 2θ with respect to the angle θ, the polarization rotation angle can be arbitrarily determined, whereby the transmittance of the PBS can be adjusted from 0% to 100%.
The final adjustment of the light quantity ratio between Ch-A and Ch-B may be used.

After the merged channels pass through the beam expander as described above, they are condensed on the glass master 6 by the objective lens 5 to form respective spots. The spots of both channels are a small distance in the radial direction (generally, within 1/2 of the track pitch = maximum 1)
(about μm). This adjustment is
From the state where the optical axes of both channels after the merging are completely coincident, the appropriate “tilt angle” for the PBS 11 so that the reflection angle of the Ch-B on the PBS 11 is inclined by a required amount in the radial direction.
It is done by giving.

When the present invention is carried out by the above optical system, for example, a pit is exposed by giving the same recording signal as usual to a Ch-A modulator, and a DC signal is given to a Ch-B modulator. To expose the groove. At this time, Ch-A and Ch-A
The adjustment is performed so that the spot of -B is almost exactly 1/2 track apart in the radial direction at the photoresist surface focus position.

However, although it was possible to form finer pits by the two-beam pit exposure method described above, the reproduction signal characteristics did not improve as expected.
It was almost the same as ordinary one-beam recording.

Specific numerical values will be introduced.

* Experiment 1 “Comparison of reproduction signal characteristics between one-beam exposure pit train and two-beam exposure pit train” [Recording optical system] Recording wavelength λ = 351 nm NA = 0.
90 [Recording signal] EFM signal Linear density: 0.17 μm /
bit T. P = 0.47 μm [Reproduction optical system] Reproduction wavelength λ = 635 nm NA = 0.
94 [Result-Reproduced Signal Jitter Value] 7.9% for 1-beam recording: Result 1-1 7.8% for 2-beam recording: Result 1-2 (Jitter: Reproduced signal time-axis fluctuation. A small value is preferable. It is considered that the cause is that the bottom surface of the land pit formed by performing the two-beam recording has a larger fluctuation of the boundary than the normal pit at the time of the one-beam recording and is formed unstable. You. That is, crosstalk (leakage of adjacent track signals) during reproduction is reduced because the pits are formed to be thin, but the large variation in the shape of each pit itself is improved to the extent that jitter is expected. It is likely that there is no reason.

Normally, when recording with one beam, the cross section in the radial direction of the pit P is such that the length at the interface between the glass master 6 and the photoresist 9 is the upper bottom w1, and the length at the surface of the photoresist 9 is the lower bottom w2. <W2 is approximated by a trapezoid,
When viewed in detail, the side walls generally intersect linearly with the upper bottom side, but intersect with the lower bottom side in a curved manner while drawing an arc so as to draw a skirt (see FIG. 6).

This reflects the fact that the light intensity of the exposure spot has a Gaussian distribution that decreases as going outward from the center of the spot. At the bottom, the boundary line is ambiguous, and the influence of light intensity change due to noise or the like is large, and the boundary becomes unstable. On the other hand, the boundary of the trapezoidal upper bottom is formed clearly and more stably.

For this reason, while the bottom surface of a pit usually has a clear boundary, the land pit is inverted, so that its head plane is formed by an unstable boundary line. It can be considered that the signal reproduced by the reflected light from these surfaces has the effect.

As described above, land pits formed by two-beam recording can be formed finer than normal pits using the same light source and objective lens numerical aperture. Due to this, the pit head plane boundary is formed unstable and the variation of each shape becomes large, so that the reproduction signal does not improve as long as expected.

Therefore, in order to realize high recording density accompanied by improvement of reproduction signal characteristics using the two-beam recording method, it is required to solve this problem by some means.

As a method for solving such a problem, first, optimization of the pit shape can be mentioned.

In the two-beam exposure method, the width and length of the pit can be independently adjusted by changing the exposure intensity of the two spots, and the pit shape is further optimized as compared with the conventional one-beam exposure method. It is possible to

That is, if the pit shape is manipulated only by the exposure intensity of one beam, the pit shape is limited to “long and thick pits” or “short and narrow pits” at the maximum. Long and narrow pits and short and thick pits can also be formed.

As the density of an optical disk increases, the pit shape needs to be optimized more precisely.

Here, considering the relationship between the pit width and the reproduction signal, if the pit is too thick, the signal leakage (crosstalk) from the adjacent track increases during reproduction, causing an adverse effect. After that, the amplitude of the reproduction signal decreases (= the modulation degree decreases).

In consideration of the relationship with the pit length, the narrow pits need to be longer in order to satisfy the asymmetry appropriate for reproduction. As a result, the interval between adjacent pits in the tangential direction decreases. Therefore, signal leakage from them increases (inter-symbol interference increases).

For these reasons, the range of the optimum pit width when a certain recording density is given is limited.
This range was determined experimentally using a two-beam exposure method.

Hereinafter, in the three recording densities described below, 2
The pit width and length were adjusted by independently adjusting the beam exposure intensity, and the optimum value of the pit width was determined for each. The results are shown in Tables 1 to 3.

Table 1 shows that the recording signal is an EFM signal and the track pitch T.D. P is 0.50 μm, linear density is 0.18
Table 2 shows the recording signal as an EFM signal and a track pitch T.P. P is 0.47μ
m, the linear density is 0.17 μm / bit,
Table 3 shows that the recording signal is the EFM signal, the track pitch T.V. P
Is 0.41 μm and the linear density is 0.15 μm / bit.

The reproduction jitter value is described by selecting the best value (minimum value) from several data obtained by changing the pit length depending on the intensity of the pit exposure side spot in each land pit width.

All of these exposure optical systems have a recording wavelength λ = 3.
51 nm and the objective lens NA = 0.90. In addition, a pre-development process described later is employed.

The disk used in the evaluation was formed by injection molding from a mother stamper to a polycarbonate substrate having a thickness of 1.1 mm, forming an aluminum reflective film to a thickness of 15 nm on the signal surface by a sputtering method, and starting from the surface. Thickness 0.1
This is a type in which reproduction light is irradiated through a transparent protective layer having a thickness of 2 mm.

At this time, the length and width of the pit are reduced by about 10 nm from those transferred onto the substrate by being filled with the reflection film. Therefore, the pit width described here is a value obtained by subtracting 10 nm from the value obtained by actually measuring the substrate (both the upper bottom portion W1 and the lower bottom portion W2) with an electron microscope. Note that the pit width narrows in short pits such as 3T and 4T of the EFM signal, but is measured in a sufficiently long pit.

The reproducing optical system has a reproducing wavelength of 635 nm, an NA of
0.94.

[0079]

[Table 1]

[0080]

[Table 2]

[0081]

[Table 3]

In Tables 1 to 3, pit width / T. The pit width in the column of P is a value represented by (W1 + W2) / 2.

From the results at each recording density, the pit width Wm [= (W1 + W2) / 2] is equal to the track pitch T.D. For T.P. P × 0.40 ≦ Wm ≦ T. P × 0.50... It has been found that it has an optimum value in the range of Expression 2.

For reference, a DVD (EFM signal, TP = 0.
The pit width when the lowest jitter value was obtained by one-beam exposure of 74 μm and a linear density of 0.27 μm was:
43% of the track pitch, suggesting that the range of Equation 2 is approximately generally valid.

In order to satisfy the above equation 2 using the two-beam exposure method, the width Wg of the groove exposed on the side of the pit is required.
(Wg is the average value of the upper and lower bases of the trapezoidal radial cross section of the groove. That is, Wg = TP−Wm). P × 0.50 ≦ Wg ≦ T. P × 0.60 Expression 3

As described above, in the case of the disk structure of the present example, the pits are narrowed by about 10 nm by the reflection film. When P = 0.3 to 0.5 μm, it corresponds to 2 to 3%, but is ignored because it is not in a range that greatly deteriorates the reproduction signal.

In order to realize a high recording density accompanied by an improvement in the reproduction signal characteristics by using the two-beam recording method, the present invention is further directed to a method of forming a land pit head plane in a stable manner. A process of forming a hardly soluble layer on the surface of the resist by dipping the resist surface in a developer (hereinafter referred to as a pre-development process) was employed.

This pre-development process is also called a surface insolubilization treatment. For example, in the case of a diazo-based resist, the unexposed resist is immersed in an alkali developing solution or solution, washed with water, and dried.

Alternatively, it may be carried out through a step of bringing the resist surface into contact with water to improve the wettability, a step of bringing a developer or a diluted developer into contact with the surface of the resist, and a washing step.

Examples of the alkali developer include an aqueous solution of trimethylammonium hydroxide (TMAH) and an aqueous solution of a mixture of sodium phosphate and disodium hydrogen silicate.

The same effect can be obtained by immersing the diazo resist in chlorobenzene for several minutes.

By this process, the inclination angle of the side wall is generally improved (approximately vertical) in the commonly used novolak-based photoresist, and the intersection of the lower bottom portion of the pit with the side wall, which was a problem (see FIG. 7A) is also improved until it has almost the same clear border as the upper bottom (see FIG. 7).
B).

As a result, (1) the boundary line of the land pit head plane is formed stably, so that variations in individual pit shapes are reduced. (2) As the pit inclination angle is improved, the area of the head plane increases without increasing the width of the lower bottom of the land pit.
The pit shape is further stabilized in combination with (1). Alternatively, when the area of the head plane does not change, the width of the bottom of the pit decreases, so that crosstalk and intersymbol interference are reduced, and the reproduction signal characteristics are improved. The pit recording method using two-beam exposure achieves a higher recording density.

The reason why such a phenomenon occurs due to the insoluble layer formed on the photoresist surface will be briefly described.

The hardly soluble layer is a region where the development is suppressed. In other words, since the sensitivity is low there, it is barely dissolved only in a region narrower than the region where normal development proceeds, that is, in a region closer to the center of the spot and having a high exposure intensity. When the hardly soluble layer on the surface is removed, the photoresist immediately below is sufficiently exposed to light, so that the development reaches the glass surface at once.

With such a mechanism, a pattern having a nearly vertical cutting angle is formed.

An example in which the reproduction signal characteristic is improved by introducing this process will be described. Under the same conditions as in Experiment 1, 2
At the time of beam recording, only a pre-development process was added to produce a disk.

* Experiment 2 “Pre-development process + reproduction signal of two-beam exposure pit train” [Recording optical system] Recording wavelength λ = 351 nm NA = 0.
90 [Recording signal] EFM signal Linear density: 0.17 μm /
bit T. P = 0.47 μm [Reproduction optical system] Reproduction wavelength λ = 635 nm NA = 0.
94 [Result-Reproduced Signal Jitter Value] Pre-development (20 s) + two-beam exposure: 7.3%: Result 2 As described above, the jitter value was obtained by adding the pre-development process as compared with Result 1-2. 7.8% to 7.3%
Was confirmed to have decreased.

Even when this pre-development process is introduced during normal one-beam exposure, there is a possibility that the reproduction signal characteristics may be improved mainly due to the reason (2). Therefore, it was verified in Experiment 3. This is also the same condition as in Experiment 1.

* Experiment 3 “Pre-development process + 1 Reproduction signal of beam exposure pit row” [Recording optical system] Recording wavelength λ = 351 nm NA = 0.
90 [Recording signal] EFM signal Linear density: 0.17 μm /
bit T. P = 0.47 μm [Reproduction optical system] Reproduction wavelength λ = 635 nm NA = 0.
94 [Result-Reproduction signal jitter value] Pre-development (20 s) +1 beam exposure: 7.7%: Result 3 Jitter is almost the same as when pre-development is performed (Result 1-1) and combined with two beams The improvement effect was not seen as much as in the case of. This is because, in one-beam exposure in which exposure at a low intensity is performed to form pits minutely, the dissolution of the hardly-soluble layer becomes unstable, the pits become thinner, and crosstalk and the like are reduced. This is presumed to be due to the offset.

On the other hand, in the case of the two-beam exposure, the grooves on both sides of the pits are formed thicker than the pit width of the one-beam recording, so that the exposure is performed at a higher intensity.
As a result, it is considered that the hardly soluble layer was stably removed.

Further, with respect to the correlation between the pit forming method described above and the reproduction signal characteristics, an experiment was conducted to confirm the tendency at a higher recording density. However, the evaluation of the combination of two-beam exposure and no pre-development was not performed because the shortest pit (pit length = 0.22 μm) could not be formed. Note that the reproduction wavelength λ was shortened from 635 nm to 532 nm in response to the increase in density.

* Experiment 4 “Correspondence between each pit forming method and reproduction signal when density is further increased” [Recording optical system] Recording wavelength λ = 351 nm NA = 0.
90 [Recording signal] EFM signal Linear density: 0.148 μm
/ Bit T. P = 0.41 μm [Reproduction optical system] Reproduction wavelength λ = 532 nm NA = 0.
94 [Result-Reproduced signal jitter value] 1-beam exposure: 8.6%: Result 4-1 Pre-development (20 s) +1 beam exposure: 8.6%: Result 4-2 Pre-development (20 s) At the time of +2 beam exposure: 7.9%: Result 4-3 The same tendency was observed.

As has been seen above, the RO beam can be obtained by combining the two-beam pit exposure method with the pre-development process.
M high-density recording became possible. Then, it was found that this pre-development process exhibited a greater effect when combined with two-beam exposure than when combined with normal one-beam exposure.

[0105]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each process of actually manufacturing an optical disk substrate using the pit forming method of the present invention will be described below.

(1-1) Glass Polishing and Photoresist Coating Steps are performed in the same manner as in the related art.

(1-2) Pre-development step In the same manner as in a normal development method, (1) rinsing of the surface → (2) immersion under the developing droplet or in the developing solution → (3) rinsing again.

The development time may be about 10 to 30 seconds. As the pre-development time is longer, the pit inclination angle tends to approach vertical, but it is empirically known that the effect of the pre-development time difference of about 5 seconds on the pit shape is so small that it can be ignored. There is no problem about. In the experiments described in this invention report, the photoresist was commercially available I
-Novolak resin positive resist for wire, inorganic alkaline developer as a developer, manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name DE-
4 is used.

(2) Exposure Step (Cutting) As described above, the cutting optical system is a two-beam system as shown in FIG. 5, and a normal pit pattern is exposed by one of the exposure spots, and is substantially (1/1 /) in the radial direction. The groove is exposed at the other spot at a distance of (2 × track pitch).

The interval between the two spots is (1/2 + n) × track pitch (n = 1, 2) for easy adjustment.
2,3. . . ).

This is because there is no measuring instrument (such as an optical microscope) that can easily and accurately measure the distance between the two spots when it is 0.50 μm or less.

(3) Developing step The developing step is carried out in the same manner as in the prior art.

(4) Stamper Manufacturing Step In the stamper S, the land pits LP are inverted from the regular pits P shown in FIG. 8 (FIG. 9). Is desired to have the same irregularities as usual. Therefore, when using a positive resist generally used for optical disk applications (a type in which exposed portions are dissolved after development), Ni plating is applied again to a master stamper made by Ni plating on a glass master and transferred. It is necessary to use a mother stamper in which the unevenness is reversed again.

The reason why the stamper is required to have the conventional unevenness for the injection molding, that is, the pit must be convex will be described below.

In general, in injection molding, the transfer becomes more difficult as the area of the concave portion of the stamper decreases. For example, in the case of a stamper having a groove structure, as the width of the groove (laser exposed portion) increases, the area of the concave portion decreases, and normal transfer becomes difficult.

FIG. 10 shows the result of an experiment conducted on this. This is T. P = 0, 85 μm, groove depth d =
Regarding the stamper of 120 nm, the transferability when polycarbonate (PC) usually used for an optical disk is used as a substrate material is represented by the horizontal axis = the area ratio occupied in the entire concave portion (=
(Groove width / track pitch), vertical axis = groove depth on PC after molding. The mold temperature that most affects the transferability was used as a parameter.

It can be seen that although the temperature is slightly improved by increasing the mold temperature, the transfer of the groove becomes incomplete as the area occupied by the concave portion on the stamper decreases.

The reason why such a phenomenon occurs is that in the process of filling the concave portion with the molten plastic resin, the narrower the gap is, the more difficult it is to enter that portion.
When the pit row is concave on the stamper, the transfer is more difficult because the ratio of the concave portion to the entire area is further reduced because the pit row is discontinuous in the line direction as compared with the groove. As shown in the experimental results of FIG. 10, the transferability is improved by increasing the mold temperature, but the temperature cannot be increased excessively in practical use. A major reason for this is that, in general, the warpage of the molded substrate increases as the mold temperature increases. The warpage of the substrate is recorded on the signal surface /
This impairs the light-collecting property of the reproduction spot and is a major factor in deteriorating the recording / reproduction signal. In addition, since the mold itself expands as the temperature becomes higher, the operation of the mold may be hindered and the accuracy may not be guaranteed. In the worst case, the device may be damaged by galling of the movable part.

In view of the above, it can be empirically found that the upper limit value of the mold temperature is about 130 ° C. which is shown in the experimental results. It is expected that there is.

Although there are parameters that contribute to transferability under other injection molding conditions, there is no parameter that has such a large effect as to enable this transfer.

Therefore, in the case of a land pit, since it becomes concave on a normal stamper, it is necessary to manufacture the above-mentioned mother stamper in order to secure transferability during injection molding. By the way, in the format of the optical disk conventionally manufactured, there is no case where the pits are reversed on the stamper.

FIG. 11 shows a method of manufacturing a mother stamper.
Will be described.

First, an ordinary process for producing a master stamper is performed after a Ni master plating is applied to a glass master and then peeled off.

That is, as described above, a layer of a positive photoresist 52 is formed on a glass master 51, and a recording laser beam is irradiated from an objective lens 53 to form a latent image of a groove and a latent image of a land pit. (Exposure step).

Next, this is developed (development step), and Ni plating 54 is applied. The Ni plating 54 is peeled off to form a master stamper (master stamper manufacturing step).

Thereafter, when manufacturing the mother stamper from the master, first, in order to improve the releasability between them, a release coating 55 forming process such as a surface oxidation treatment using a dichromic acid solution is required. After this process, a Ni layer 56 is formed on the master by electroplating,
This is peeled off.

The above-described stamper-to-stamper transfer process is currently generally used for CD manufacturing. At this time, a grandchild stamper was further prepared from the mother stamper by the same method and used for injection molding. Since a plurality of mothers can be produced from a master and a plurality of stampers can be produced from a mother, they are used for mass production of substrates from one cutting. Also in this process, it is possible to manufacture a plurality of mother stampers from the master stamper to improve productivity.

Further, even if the transfer is performed an even number of times from the mother stamper, the relationship between the pits and projections does not change, so that they can be used for injection molding.

When a negative type photoresist (a type in which an unexposed portion is dissolved after development) is used, land pits are convex on the master stamper. There is no need to reverse the irregularities. However, for the purpose of producing a plurality of stampers for mass production, a stamper produced by an even number of transfers from a master stamper may be used.

(5) Substrate Fabrication Step Injection molding is performed on a plastic substrate (for example, polycarbonate used for CD and DVD) from the stamper having the convex land pits obtained in the above process.

Thereafter, a reflective film of Al or the like is formed on the pattern surface of the substrate.

Thereafter, an ultraviolet curable resin (UV resin) is applied as a protective film on the Al film with a spinner and cured with ultraviolet light to complete the disk. Also, UV
A method of bonding plastic sheets of the same thickness instead of applying resin is also conceivable.

In the CD, the UV resin layer was used only as a protective film, and the reproduction light was emitted from the opposite surface. On the other hand, in the next-generation high-density optical disk, it is certain that the NA of the reproduction objective lens is increased, and the defocus and the accompanying
In order to reduce remarkable deterioration of the reproduction signal when the disk is tilted, it is expected that the irradiation of the reproduction light is performed from the UV resin layer side where the optical path length in the disk becomes short. In this case, the thickness of the plastic substrate is 1.0 to 1.2 mm, U
The V-resin layer thickness will be on the order of 0.1 mm.
The disks for which the experimental results were described earlier were all 0.1 mm thick.
Was reproduced from the UV resin layer side.

If the NA of the objective lens is about the same as that of a DVD (around 0.60), the thickness of the plastic substrate is set to about 0.6 mm, and the plastic substrate is bonded to another plastic substrate of the same thickness with an adhesive layer interposed therebetween. Is applied.

The reproduction signal measurement results of the disk manufactured by the above manufacturing process are as described above.

Now, as means for high-density recording, RIE (Reactive Io) using a resist pattern as a mask.
n Etching) processing method has been proposed. RIE
In the apparatus, as shown in FIG. 12, a high voltage is applied between two plane electrodes connected to a high-frequency power supply 61 to generate plasma in a reactive gas in a container. The generated gas ions are vertically incident along the electric field on the surface of the sample (the synthetic quartz substrate 62 on which the photoresist layer 63 is formed) placed on one of the electrodes, where a chemical reaction occurs and etching occurs. Proceed vertically.

The advantages are an etching characteristic close to vertical, selectivity of an etching substance due to a chemical reaction, and high productivity which is a characteristic of dry etching.

When this is used, in the resist pattern, the upper bottom side of the pit is smaller than the lower bottom side, so that the pit formed by etching using the upper bottom side as a mask is further reduced, and the inclination of the pit is reduced. Can be cut almost vertically, which is convenient for high-density recording. The two-beam exposure method also has the following advantages over this RIE process.

[0139] 1. Normal pits are formed as recesses on a resist serving as a mask, but normal etching becomes more difficult as densities of pits increase. The reason is that when ions serving as an etching source are incident on a narrow hole, the probability of collision with the resist wall surface is increased and it is difficult to reach the bottom surface. As a result, in a short pit in the pit pattern, the progress of etching is slowed, and the pattern variation increases.

On the other hand, since land pits are convex on the resist, the above problem does not occur, and ultra-high density can be easily achieved.

[0141] 2. Generally, pits vary in width depending on their length. A pit having a length shorter than the exposure spot diameter is narrower than a pit having a longer length. On the upper and lower bottom sides of the pit, the width changes are particularly strong on the upper bottom side. This is the same in the land pit. Therefore, in the case of a normal pit using the upper bottom side as a mask, the pit length dependency of the pit width is emphasized after etching as shown in FIG. 14).

As a result, the short pits are formed firmly with almost the same width as the long pits, so that the degree of modulation during reproduction is increased and jitter is reduced. Since the lower bottom side is used as a master, it is not possible to make the etching pattern finer than the resist pattern, but there is no problem since the land pits can be originally formed sufficiently small. On the contrary, it is considered that the effect is great when short pits that have become too small are used for the purpose of reforming them to a required size by etching.

The two-beam exposure method and R
An actual disk manufacturing process combined with IE processing will be described.

Disk Manufacturing Process Using RIE (1) Resist Step The glass master is desirably made of synthetic quartz (SiO ₂ ) containing no impurities in order to stabilize etching.

Regarding the surface treatment for improving the adhesiveness with the resist, similarly, in order to prevent impurities from adhering to the interface between the resist and the glass, a treatment with a chemical such as HMDS is performed instead of sputtering of Cr atoms or the like. Is good.

Of course, the present invention is not limited to this, and various substrate materials can be selected according to the etching method.

As etching methods that can be considered for optical disk pit processing, (1) RIE utilizing a chemical reaction between etching gas ions and the surface of an etching object
There are a (reactive ion etching) method and (2) an ion milling method in which physical etching is performed by impact when ions collide with the surface of an etching target. However,
The RIE method is preferable because the RIE method has an advantage that a resist pattern serving as a mask does not need to be etched much, and the ion milling has a disadvantage that repelled atoms easily adhere to the surface.

For example, in the case of the RIE method, the following substrate materials can be used.

Si (silicon): Etching is possible with a halogen-based gas such as F ₂ and Cl ₂ and a chlorofluorocarbon-based gas such as CF ₄ and CHF ₃ SiO ₂ (synthetic quartz), Ta (tantalum), W (tungsten), Pt (platinum): Etching is possible with a chlorofluorocarbon gas such as CF ₄ or CHF ₃ Mo (molybdenum): Etching is possible with a fluorine-based gas such as F ₂ Al (aluminum), Cr (chromium), Ti ( Titanium), Au (gold) ... Can be etched with chlorine-based gas such as CCl ₄ , C ₂ Cl ₂ F _{4 In the} ion milling method, any substance in principle including general metals such as chromium and nickel But it can be etched.

Although etching can be performed mainly by the above combination, when exposing the resist pattern prior to the etching, if the base is made of a metal having a high reflectance, it is difficult to perform appropriate exposure due to the influence of reflected light. Further, since Si or the like is brittle, there is a possibility that it cannot withstand the subsequent transfer process.

Therefore, in optical disc applications,
A combination of synthetic quartz and RIE is preferred.

(2) Pre-development step The pre-development step is not always necessary, but it is desirable to perform the pre-development step because it can reduce minute fluctuation at the pit boundary.

(3) Exposure and Development Step The pit pattern is exposed and developed by a two-beam exposure method.

(4) Post-bake Step In order to improve the durability of the resist against etching, baking is usually performed after development. On a hot plate, conditions of 100 to 120 ° C. for several minutes are common.

(5) RIE Step When the target of etching is SiO ₂ , CF ₄ or CHF ₃ is used as a reactive gas. The following is an example of various etching conditions.

[0156] Vacuum achievement: 10- ³ Pa · gas pressure: 3.0Pa / gas flow rate: 10sc
cm ・ High frequency RF power output: 200 W (frequency 13.56
MHz) Under the above conditions, an etching rate of 20 to 30 nm / min was obtained. Since the pit depth required for a ROM disk is 50 to 100 nm, a desired depth can be obtained by etching for several minutes.

(6) Resist Removal Step Since the resist mask after etching is deteriorated under plasma, it cannot be easily removed with a developing solution or an organic solvent such as acetone. Therefore, a method (ashing) of burning the remaining resist with O ₂ plasma is usually used.

By the above processes, the production of the glass master having the pit pattern formed by etching is completed.

(7) Stamper Manufacturing Step A stamper can be manufactured from the above-mentioned glass master by a Ni plating process in the same manner as in a normal process. However, unlike the resist surface, Ni does not adhere to the glass surface, so that a process of dropping a coupling agent such as silane on the glass surface is required. Also in this case, since the pits are concave on the master stamper (when a positive resist is used as a master), it is necessary to manufacture a mother stamper.

(8) Disk Manufacturing Step After the injection molding, the process is the same as the above-mentioned process.

Further higher density can be realized by combining the RIE process, which is one of the fine pit forming techniques, with the two-beam exposure method capable of solving the problem for the above-mentioned reason.

Next, the design of the pit width in the resist mask pattern when the RIE etching process is introduced will be described.

When introducing an etching process,
Consider that the pit width to be formed falls within the range of Equation 2 obtained earlier. In this case, since the shape of the pit formed by etching does not match the shape of the pit drawn on the resist, it is necessary to change the exposure condition from the normal condition.

Taking into account the cross-sectional shape of the pit or groove after etching and the amount of etching progress in the width direction caused by the spread of the opening of the photoresist mask, the width of the pit to be drawn on the photoresist, that is, the DC width in the two-beam cutting exposure, The groove width drawn by the spot on the irradiation side can be determined as follows.

First, regarding the cross-sectional shape of the pattern after etching (FIG. 15), it can be considered that the inclination angle θ of the side wall is almost within 75 ± 5 degrees. The range that can be taken as the pit height d is 60 nm ≦ d ≦ 120 nm.
Assuming that the width at the photoresist mask interface is W2 ′, the trapezoidal approximation of the cross-sectional shape of the region formed by etching below (= the region sandwiched between the land pits) results in a width Wm at a bisecting height. ′ (= Average value of trapezoid upper base W1 ′ and lower base W2 ′) is d = 12 when the above condition is used.
Wm '= W2'-4 at the minimum when 0 nm and θ = 70 deg
4 nm, and Wm '= W2'-11 nm at the maximum when d = 60 nm and θ = 80 deg. That is, W2′-44 (nm) ≦ Wm ′ ≦ W2′-11 (nm)...

Next, the amount of etching progress in the width direction at the opening of the resist mask will be considered. The side wall of the resist pattern has a tilt angle of about 60 to 70 degrees, and the remaining resist becomes thinner as it approaches the opening. Therefore, as the resist itself is etched down to the surface of the master, the mask gradually increases, and eventually the width W2 'at the opening of the etching pattern becomes wider than the original width Wa of the mask opening (FIG. 16). .

The width expansion amount ΔW = W2′−Wa is given by
The number decreases as the resist is hardly etched. The etching rate Ve of the object to be etched with respect to the etching rate Vr of the resist is generally called a selectivity, and this value is an index for estimating ΔW.

Therefore, the following RIE experiment was performed.
ΔW was estimated.

Experimental Conditions ・ Etching object: Synthetic quartz (SiO ₂ ) ・ Photoresist: Commercially available G-line Coating thickness 2000Å (Pattern side wall inclination angle at this time is about 70 degrees) ・ RIE condition: Etching gas CF ₄ gas pressure 3.0 Pa Gas flow rate 10 sccm Etching time 210 seconds High frequency power output 200 W Experimental result ・ Etching depth d = 56 nm ・ Selection ratio (SiO ₂ etching rate: resist etching rate) = 1.6: 1.0 Groove width in resist pattern ( A plurality of (opening widths) were provided, but all had ΔW = about 30 nm.

In practice, it is unlikely that etching is performed with a value smaller than the selectivity of 1.6. The reason is,
The resist must be applied thicker, which causes the problem of dissolving the resist due to the increase in heat accumulation during exposure, and the inclination angle of the etching pattern is reduced, which is contrary to the purpose of high density. is there. Therefore, the traveling speed in the width direction in this experiment is regarded as the maximum.

The minimum value of ΔW can be considered to be zero because the selection ratio can be made sufficiently large by the kind of gas, pressure, and high-temperature baking of the resist.

Considering that ΔW is proportional to the etching depth, the following equation was obtained from these: 0 (nm) ≦ ΔW ≦ (30/56) × d (nm)

In conclusion, considering Equations 4 and 5, the width Wm 'of the etching pattern is expressed as follows: Wa−45 (nm) ≦ Wm ′ ≦ Wa + 45 (nm) with respect to the width Wa of the opening of the resist pattern serving as a mask. .... It should be within the range of Expression 6-1. In other words,
When Wa is given, it indicates that there is an etching condition that can form Wm ′ within a range satisfying the above equation by adjusting the depth, the inclination, and the selectivity.

Conversely, when Wm 'is specified, the range of Wa must be as follows: Wm'-45 (nm) ≤Wa≤Wm' + 45 (nm) Equation 6-2 .

According to the estimation of the pit width optimum value performed earlier, in order to obtain an optimum reproduction signal, the land pit width Wm should be set to 40% or more and 50% or less of the track pitch. When using the two-beam exposure method, what is etched away is not the land pits, but the region existing between the tracks, that is, the side where the groove was exposed, and the groove width in the above equation W
m ′.

Therefore, according to Equations 3 and 6-2, when etching is performed using the resist pattern formed by the two-beam exposure as a mask, the groove side width Wa (= cross section of the resist pattern in the resist pattern opening) is obtained. The upper base W1) of the trapezoid is set to the track pitch T. With respect to P, (TP × 0.50) −45 (nm) ≦ Wa ≦ (TP × 0.60) +45 (nm)... It is possible to form a land pit having

[0177]

As described above, by using the mastering master manufacturing process of the present invention, a higher density optical disc can be manufactured without changing the light source of the exposure apparatus or the numerical aperture of the objective lens.

In addition, RIE (Reactive Io) conventionally proposed as one of the fine pit formation techniques.
n Etching) process has problems,
The problem is solved by forming a master resist pattern by two-beam exposure. By combining these, it is possible to further increase the density by a synergistic effect.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration example of an exposure apparatus.

FIG. 2 is a schematic diagram showing a basic optical system of the exposure apparatus.

FIG. 3 is a schematic view showing a normal exposure spot and pits formed by the exposure spot.

FIG. 4 is a schematic diagram showing an exposure spot in two-beam exposure and land pits formed by the exposure spot.

FIG. 5 is a schematic diagram illustrating an example of a two-beam optical system used for two-beam exposure.

FIG. 6 is a schematic diagram showing a radial cross section of a pit formed by one-beam exposure.

FIG. 7 is a schematic diagram showing a difference in a pit shape depending on the presence or absence of a surface insolubilization treatment.

FIG. 8 is a schematic perspective view showing a normal pit formed on a stamper.

FIG. 9 is a schematic perspective view showing land pits formed on a stamper.

FIG. 10 is a characteristic diagram showing the relationship between the occupied area ratio of the concave portion and the groove depth after transfer.

FIG. 11 is a schematic cross-sectional view of a main part showing a step of manufacturing a master stamper and a mother stamper.

FIG. 12 is a schematic diagram illustrating an RIE processing method.

FIG. 13 is a schematic diagram showing the pit length dependence of the pit width after normal pit etching.

FIG. 14 is a schematic diagram showing a pit length dependency of a pit width after land pit etching.

FIG. 15 is a schematic diagram showing a cross-sectional shape of a region etched and formed by RIE.

FIG. 16 is a schematic diagram showing the spread of a mask opening as etching proceeds.

FIG. 17 is an external perspective view of an optical disc.

FIG. 18 is a schematic perspective view showing a pit shape of a conventional optical disc, partially broken away.

FIG. 19 is a schematic perspective view showing a groove structure of a conventional optical disc with a part thereof cut away.

FIG. 20 is a diagram illustrating a conventional optical disk substrate manufacturing process.

[Explanation of symbols]

1 laser light for recording, 5 objective lens, 6 substrate, 9
Photoresist, LP land pit

Claims (8)

[Claims] 1. A step of forming a photosensitive layer on a support, a step of exposing a predetermined area of the photosensitive layer, and a step of developing after exposure to form a concavo-convex pattern corresponding to a pit row pattern on the photosensitive layer. Forming a concave and convex portion related to recording and / or reproduction of information on the base based on the concave and convex pattern, wherein the first light spot for exposing the pit pattern; The first light spot is substantially n / track pitch in the radial direction.
A second exposure of a groove that partially overlaps the side of the pit pattern at a distance of 2 (where n is an integer)
When the photosensitive layer is exposed to the light spot and the trapezoidal cross-sectional shape in the radial direction of the groove, when the groove width is given as an average value of the upper base and the lower base of the trapezoid, the value Wg is Track pitch T. P
For T. P × 0.50 ≦ Wg ≦ T. A method for manufacturing an information recording medium, wherein the method is set to be P × 0.60. 2. The method for producing an information recording medium according to claim 1, wherein the surface of the photosensitive layer is immersed in a developer to make it hardly soluble before the exposure step. 3. A positive stamper for the photosensitive layer, and a master stamper to which a concave / convex pattern formed on the photosensitive layer is transferred is manufactured.
2. The method for manufacturing an information recording medium according to claim 1, wherein a stamper obtained by an odd number of transfers is used as a mold for injection molding of a plastic substrate. 4. A step of forming a photosensitive layer on a support, a step of exposing a predetermined area of the photosensitive layer, and a step of developing after exposure to form a concavo-convex pattern corresponding to a pit row pattern on the photosensitive layer. Forming a concave and convex portion related to recording and / or reproduction of information on the base based on the concave and convex pattern, wherein the first light spot for exposing the pit pattern; The first light spot is substantially n / track pitch in the radial direction.
A second exposure of a groove that partially overlaps the side of the pit pattern at a distance of 2 (where n is an integer)
Exposing the photosensitive layer with the light spot of the above, and a step of forming the unevenness directly on the support by etching and removing the remaining resist using the photosensitive layer having the unevenness formed in the developing step as a mask, The width Wa at the boundary surface between the photosensitive layer and the support corresponding to the groove before etching is determined by the track pitch T.D. For P, (TP × 0.50) −45 nm ≦ Wa ≦ (TP ××
0.60) +45 nm. A method for manufacturing an information recording medium, characterized in that: 5. The method according to claim 4, wherein the etching is reactive ion etching. 6. The method for producing an information recording medium according to claim 4, wherein the surface of the photosensitive layer is immersed in a developing solution to make it hardly soluble before the exposure step. 7. The method for manufacturing an information recording medium according to claim 4, wherein said support is made of synthetic quartz. 8. A master stamper in which a photosensitive layer is made positive and a concave and convex pattern formed on a support is transferred,
5. The method for manufacturing an information recording medium according to claim 4, wherein a stamper obtained by an odd number of transfers is used as a mold for injection molding of a plastic substrate.