JP2000339780A - Production of master disk of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a pit and a groove having a smaller width than the limit of the diameter of a light beam for exposure determined by its wavelength and the aperture of a lens. SOLUTION: In an exposure step in which the surface of a photoresist layer 2 is exposed with a light beam whose intensity is modulated with the lapse of time in accordance with information to be recorded to record the information as a latent image 15 in the photoresist layer 2, the photoresist layer 2 is subjected to multiple exposure with a light beam 12 which regulates the width Pw of a pit 8 by the interval between two condensing spot parts 12a, 12b and a light beam 13 whose intensity is modulated in accordance with information to be recorded.

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 a master optical disc for producing a stamper which becomes a mold for producing an optical disc by injection molding of a resin or the like.

[0002]

2. Description of the Related Art Optical disks such as CDs and DVDs are large-capacity memories for recording and reproducing information by irradiating a rotating recording disk (disk medium) with a laser, and have a high recording density and a large amount of information. Because of its great portability, it has attracted attention as being able to cope with the dramatic increase in the amount of information accompanying the progress of the information society in recent years. This optical disc is generally manufactured through the steps shown in FIG.

That is, as shown in FIG. 1 (a), the main surface of a disk-shaped glass substrate 1 is polished and cleaned.
On the main surface of the glass substrate 1, a photoresist layer 2 is formed by uniformly applying a positive photoresist (photosensitive resin) and drying as shown in FIG.
Subsequently, as shown in FIG. 3C, a laser beam L that blinks in response to an information signal to be recorded is condensed and irradiated on the photoresist layer 2 by a condenser lens 3. Thus, a latent image 4 of a pit row corresponding to predetermined information is formed on the photoresist layer 2 by exposure to the laser beam L. The latent image 4 is spirally or concentrically formed at a predetermined track pitch on the photoresist layer 2 by rotating the glass substrate 1 and moving the laser beam L in the radial direction of the glass substrate 1. .

Next, as the exposed photoresist layer 2 is developed, as shown in FIG. 1D, the latent image 4 which is an exposed portion of the photoresist layer 2 is removed by a developing solution, and fine concave portions are formed. That is, pits 8 are formed. When the photoresist layer 2 on which the pits 8 are formed is dried and fixed on the glass substrate 1, an optical disk master 7 having the above-described row of pits 8 is completed.

Further, after a conductive film (not shown) is formed by plating a metal such as nickel on the photoresist layer 2 of the optical disk master 7, a glass substrate 1 having this conductive film is placed in an electroforming tank. By immersion, a thick metal layer 9 is formed on the conductive film as shown in FIG. When the resist layer 2 and the conductive film are removed after the metal layer 9 is removed from the glass substrate 1, the stamper (die) 10 shown in FIG.

Next, after the stamper 10 is attached to a predetermined position of the injection molding apparatus and the mold is clamped, FIG.
As shown, when the molten transparent resin material is injected onto the stamper 10 and the resin material is cured and taken out, the resin optical disk replica 11 having a predetermined information recording surface is formed.
Is obtained. When a reflective film is formed on the information recording surface of the optical disk replica 11 and a protective film is further formed on the reflective film, an optical disk can be obtained.

[0007]

However, in recent years,
Higher densities are also being demanded for optical disks that are said to have large capacities. In particular, when attempting to handle image information, the amount of information becomes enormous, and the capacity of existing optical disks becomes insufficient. In order to increase the recording capacity, the width of the pits 8 to be formed and the tracking grooves themselves are reduced, the pit length is reduced, and the interval between the eight pit rows corresponding to the track pitch is reduced. It is conceivable to increase the density. In order to reduce the width of the pit 8 and the width of the groove, it is necessary to reduce the diameter of the exposure beam of the laser beam L that determines these dimensions. This exposure beam diameter is
The relationship is proportional to the wavelength λ of the laser and inversely proportional to the aperture NA of the condenser lens 3. Therefore, in order to reduce the width of the pit 8 and the groove width, it is necessary to shorten the wavelength λ or increase the lens aperture NA.

However, the lens aperture NA (NA ≦ NA)
In the case of 1), the current mastering has already used the one with a value exceeding 0.9, and there is little room for improvement. On the other hand, the wavelength λ is a single mode laser that can continuously oscillate and can be narrowed down sufficiently and solves problems such as life, stability, and noise. It is inevitable to use about nm.
That is, it is difficult to reduce the wavelength λ and the lens aperture NA to be shorter than those described above and to increase the NA. On the other hand, the track pitch needs to be set to be at least larger than the width of the pit 8 or the groove width. If the track pitch is too small, the track error signal is sharply reduced, and the characteristics as an optical disc cannot be secured.

Therefore, regarding the miniaturization of pits, by forming a water-soluble organic film (photobleachable layer) on the photoresist layer, the deterioration of the pattern shape due to the deterioration of the resolution limited by the optical system is contrasted. A method of forming a fine pattern by improving by the expansion effect (Japanese Patent Publication No. 4-1610)
No. 6) and forming a photobleachable layer on a photoresist layer and installing a super-resolution mask on the master writer optical system for exposure and using a super-resolution beam with a narrowed beam diameter. A method of forming fine pits and grooves with a super-resolution beam while preventing the influence of side lobes of the super-resolution beam (see Japanese Patent Application Laid-Open No. 6-302015) has been proposed.

However, in each of the above methods, when the track pitch is reduced, so-called fogging occurs at the time of exposing an adjacent pit row, so that the contrast expanding effect of the photobleachable layer is lost. Can not achieve. That is, in the case where the track pitch is narrowed and the density is increased while sequentially exposing in the rotating state of the glass substrate, due to the inclination angle of the peripheral edge of the laser beam, the bleached areas of the photobleachable layer overlap, and the bleached area. No contrast expansion effect can be obtained between track pitches in the superimposed portion of. In other words, the contrast enhancement lithography material used to form the photobleachable layer is:
This is because, since the transmittance change behavior is irreversible, once the transmittance increases due to fading due to exposure, the photobleachable layer loses the contrast expansion effect. For this reason, crosstalk during exposure that results in a wide latent image occurs in a track exposed later, and as a result, it is extremely difficult to narrow the pitch of the exposure pattern and perform high-density lithography.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and it is possible to form pits and grooves having a minute width exceeding the limit of the exposure beam diameter determined by the wavelength and the lens aperture. It is an object of the present invention to provide a method for manufacturing a master optical disc.

[0012]

In order to achieve the above object, a method for manufacturing a master optical disc according to the present invention comprises a step of forming a photoresist layer by applying a photoresist on the surface of a substrate, Exposing the surface of the photoresist layer with a light beam whose light intensity has been modulated over time, recording an information on the photoresist layer as a latent image, and developing the photoresist to record on the substrate A developing step of forming a pit row corresponding to information, wherein in the exposing step, a light beam that regulates the width of the pit by an interval between two condensed spot portions, and a light intensity based on information to be recorded A plurality of light beams including at least a modulated light beam are subjected to multiple exposure.

In this method of manufacturing a master optical disc, the photoresist layer is exposed while the width of the pits for recording information is set according to the distance between the two light-condensing spots. It can be set irrespective of the laser wavelength and the aperture of the condenser lens, which are the limiting conditions when setting the exposure beam diameter of the laser beam small, so that it is smaller than the minimum exposure beam diameter of the conventional laser beam It is possible. Therefore, in this exposure step, a latent image capable of forming a pit having a fine width exceeding the limit based on the wavelength of the laser and the aperture of the condenser lens can be formed on the photoresist layer. And record it.

In the above invention, the light intensity is modulated based on a bimodal beam having two converging spots for determining the width of the pit and information to be recorded having a single converging spot. Preferably, the photoresist layer is exposed using a unimodal beam.

Thus, since a bimodal beam having two converging spots is used, only two types of light beams, a bimodal beam and a monomodal beam, need to be subjected to multiple exposure. In the photoresist layer, an unexposed portion with a narrow width is formed between the two converging spots of the bimodal beam, and this unexposed portion is exposed with a light beam whose light intensity is modulated based on information. By doing so, it is possible to form a pit having a fine width determined by the interval between the two converging spot portions of the bimodal beam.

Further, the bimodal beam can be obtained by condensing a light beam whose phase and amplitude are variably controlled by passing through a super-resolution filter by a lens. This makes it possible to obtain a bimodal beam having two converging spot portions by extremely simple means, and to easily set a small interval between the two converging spot portions.

Further, the light intensity between the two converging spots of the bimodal beam is set so that the photoresist layer cannot be exposed. It is preferable that an image is formed on the photoresist layer in a relative relationship located at a central portion between two condensed spots of the neutral beam.

Thus, the unexposed portion of the photoresist layer formed between the two converging spots of the bimodal beam has a positional relationship in which the monomodal beam is located at the center thereof. An unexposed portion does not occur at a location exposed by the peak beam, and a pit row corresponding to the recorded information can be reliably formed.

In the above invention, when the pit rows of the plurality of tracks are formed adjacent to each other, one of the converging spot portions of the bimodal beam is used during exposure of the track in the front row of the two adjacent tracks. It is preferable that the exposed area is overlapped with the exposure area of the other converging spot portion of the bimodal beam when exposing the track in the rear row.

Thus, it is possible to reliably prevent an unexposed portion from being formed in the photoresist layer in addition to the pit formation portion, and the track pitch is the same as the diameter of one converging spot of the bimodal beam. In addition, the width of the pit can be surely made larger than the width of the pit determined by the interval between the two focused spots of the bimodal beam.

In the above invention, it is preferable that a photobleachable film is formed on the surface of the photoresist layer, and the photoresist layer is subjected to multiple exposure with a plurality of light beams through the photobleachable film.

Thus, the photoresist layer is exposed to a unimodal beam whose contrast has been enhanced by the contrast expansion effect of the photobleachable film, so that during development, the end sidewalls are removed more perpendicularly to the substrate. You. For this reason, it is possible to form pits in which the pit length is further reduced in the photoresist layer. In addition, the pits formed on the optical disk master have a small taper at the edge due to the contrast expansion effect of the photobleachable film. Therefore, the optical disk manufactured using this optical disk master has a remarkable disc signal quality. It will be improved.

In the above means, it is preferable that the photoresist layer and the photobleachable film are respectively formed of materials having the same refractive index at the exposure wavelength.

This makes it possible to suppress the multiple reflection of light at the interface between the photobleachable film and the photoresist layer at the time of exposure, so that the surface of the pit obtained by development does not become rough, and this optical disk master is used. Thus, it is possible to prevent the quality of the disc reproduction signal of the optical disc manufactured by the above method from being degraded.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. The method for manufacturing a master optical disc according to the first embodiment of the present invention includes:
A photoresist coating step of forming a photoresist layer 2 on a glass substrate 1 shown in FIG. 8B, and a laser whose light intensity is modulated corresponding to information to be recorded on the surface of the photoresist layer 2 shown in FIG. An exposure step of exposing the beam L to record information as a latent image, and developing the exposed photoresist layer 2 shown in FIG. 1D to form eight rows of pits on the surface of the glass substrate 1 corresponding to the recorded information. The manufacturing process itself is the same as the conventional manufacturing method, but is characterized in that the exposure process is different among the above steps.

That is, in the exposure step in the method of manufacturing an optical disc master according to this embodiment, as shown in FIG.
A bimodal beam 12 condensed by a converging lens (not shown) and having two converging spot portions 12a and 12b;
A single condensing spot portion 13 condensed by a condensing lens
It is characterized in that multiple exposure is performed with the unimodal beam 13 having a. Note that the bimodal beam 12 is shown by a broken line in FIG.
This is for clearly distinguishing the illustrations 2 and 13.

The portion between the two converging spots 12a and 12b in the bimodal beam 12 is
The exposure intensity is extremely low, which makes it impossible to resolve the light spots.
The portion in between is not exposed. On the other hand, the focused spot 13a of the unimodal beam 13 is positioned such that the center forms an image relative to the center between the two focused spots 12a and 12b in the bimodal beam 12, The light condensing spot 13a exposes an unexposed portion of the photoresist layer 2 between the two light condensing spots 12a and 12b.

FIG. 1B shows two converging spot portions 12 a and 12 b of the bimodal beam 12 and a unimodal beam 13.
Photoresist layer 2 formed by one condensing spot 13a
FIG. 4 is an explanatory view showing an exposure state of FIG. 3, in which portions exposed by the bimodal beam 12 and the unimodal beam 13 are indicated by oblique lines having different directions. The bimodal beam 12 is always set to a predetermined light intensity irrespective of the information to be recorded.
It is moved while maintaining the state of exposure at 12b. That is, the bimodal beam 12 is moved with respect to the photoresist layer 2 while always leaving an unexposed portion between both the condensed spot portions 12a and 12b. On the other hand, the unimodal beam 13 is moved while the light intensity is modulated with time according to the information to be recorded, while exposing the unexposed portion remaining on the photoresist layer 2 by the condensing spot portion 13a. You.

Therefore, in this embodiment, each light condensing spot portion 12a, 1 in the positive type photoresist layer 2 is formed.
The pit 8 is formed by an unexposed portion in each of 2b and 13a.
Is formed. The width P _{W of the} pit 8 formed on the basis of the latent image 15 is determined by the distance P _D between the two converging spots 12a and 12b of the bimodal beam 12, and the pit length P _L is a unimodal beam. 13 is determined by the unexposed time due to the modulation of the light intensity.

Condensing spot 13a of unimodal beam 13
Is an existing beam shape having a minimum spot diameter determined by the wavelength λ of the laser and the lens aperture NA.
Pits 8 for recording information on the photoresist layer 2 by exposure to light
Width P _W is the two bimodal beam 12 focused spot portion 1 of
2a, is determined by a distance P _D of 12b, furthermore, the two focused spots portion 12a, the distance P _D of 12b, the wavelength of the laser that is the limiting conditions for setting a small exposure beam diameter of the laser beam L Since it can be set irrespective of λ and the aperture NA of the condenser lens 3, it can be made smaller than the minimum exposure beam diameter of the conventional laser beam L. That is, in this exposure step, the wavelength λ of the laser and the aperture NA of the condenser lens 3 are set.
Image 15 capable of forming a pit 8 having a fine width _PW exceeding the limit due to the above.

FIG. 2 is an explanatory view showing a case where tracks adjacent to a track on which eight rows of pits have been formed are sequentially exposed to form eight rows of pits. After the exposure of the eight rows of pits on the n-th track is completed, the exposure of the eight rows of pits on the (n + 1) -th track adjacent to the n-th track is performed by the one condensing spot portion 12a of the bimodal beam 12. The region 17 is positioned and set so as to overlap the exposed region 14 by the other converging spot portion 12b of the bimodal beam 12 during the exposure of the n-th track. Thereby, it is possible to prevent the photoresist layer 2 from being left unexposed at locations other than the locations where the pits 8 are formed. The track pitch T _P is the same as the diameter of the converging spots 12 a and 12 b of the bimodal beam 12, and is the same as the distance between the two converging spots 12 a and 12 b of the bimodal beam 12. than the width P _W of the pit 8 for determining at P _D can be reliably large.

The exposure with the bimodal beam 12 is performed twice by each of the condensed spot portions 12a and 12b at the time of exposing eight rows of pits of two tracks adjacent to the same area. Each focusing spot 12
The light intensities a and 12b are preferably set to a level at which the photoresist layer 2 can be exposed by two exposures.

FIG. 3 is a block diagram showing an optical disk master exposure apparatus that embodies the exposure step in the method for manufacturing an optical disk master according to the first embodiment.
In FIG. 1, a laser beam emitted from a gas laser light source 18 is reflected by a first reflection mirror 19 in an orthogonal direction, and then passes through a half-wave plate 20 to a first polarization separation element (polarization beam splitter). 2.) A two-beam split into two beams at a light intensity determined based on the half-wave plate 20 and split into two beams from the first polarization splitting element 21 and a bimodal beam system 22 and a unimodal beam. Each of the light beams is emitted to the neutral beam system 23.

The light beam emitted to the bimodal beam system 22 is reflected again in the orthogonal direction by the second reflection mirror 24, and then recorded by the first optical modulator 27 comprising a high-speed optical shutter. Irrespective of the phase, is modulated so as to always have a constant light intensity. Further, the light is transmitted through the super-resolution filter 28, the phase and the amplitude are controlled, and the light is incident on the second polarization separation element 29. The light beam of the bimodal beam system 22 is controlled in phase and amplitude by passing through the super-resolution filter 28, and is then condensed by an objective lens 34, which will be described later. The bimodal beam 12 shown in FIG. 2 will be described. The super-resolution filter 28 will be described later.

On the other hand, the light beam emitted to the unimodal beam system 23 has its light intensity modulated with time in accordance with information to be recorded by the second optical modulator 30, and then the light polarization element 3
After passing through 1, the light is again reflected in the orthogonal direction by the third reflection mirror 32 and enters the second polarization separation element 29. After the light beams of the bimodal beam system 22 and the unimodal beam system 23 are recombined by the polarization splitter 29, an objective lens (condensing lens) 34 provided on a movable optical head 33. Incident on. The objective lens 34 is a dual beam system 2
By focusing each light beam from 2, 23,
The two converging spot portions 12a shown in FIGS.
A bimodal beam 12 having 12b and a unimodal beam 13 having a single focused spot 13a are formed and imaged on the surface of the photoresist layer 2 on the glass substrate 1.
At this time, the above-mentioned light polarizing element 31 outputs the unimodal beam 13.
Is precisely positioned so that the center of the condensed spot portion 13a of the bimodal beam 12 is in a positional relationship relative to the central portion between the two condensed spot portions 12a and 12b. Set to image.

The glass substrate 1 having the photoresist layer 2 on its upper surface is rotated by a spindle 37. At the same time, the optical head 33 moves the objective lens 34 from the peripheral end of the glass substrate 1 toward the center in a predetermined direction. Move at moving speed. Thereby, the photoresist layer 2 has
Eight rows of pits for each track as described with reference to FIGS. 1 and 2 are formed in a spiral shape.

Next, the super-resolution filter 28 will be described with reference to FIG. (A) to (c) of FIG.
FIG. 3 is a diagram showing the shapes of three types of super-resolution filters 28A to 28C. In each of the super-resolution filters 28A to 28C, the amplitude (light intensity) or phase distribution of a light beam incident on the objective lens 34 is changed. ing. In the super-resolution filter 28A of (a), a half of the circle is a light shielding portion,
The amplitude of the light beam is changed by the light-shielding portion, and the phase of the light beam is shifted by を wavelength (π) to be incident on the objective lens 34. The super-resolution filter 28B of (b) changes the amplitude of the light beam by two opposing fan-shaped light-shielding portions, and shifts the phase of the light beam by 波長 wavelength (π) to the objective lens 34. It is intended to be incident. The super-resolution filter 28C of (c) has two opposing fan-shaped light-shielding portions and a circular light-shielding portion at the center, and applies a light beam to each of the remaining two opposing fan-shaped light-transmitting portions by π. And by -π.

Any of the above super-resolution filters 28A-28
C, these super-resolution filters 28A to 28A-2
When the light beam changed by transmitting 8C is condensed by the objective lens 34, a bimodal beam 12 having a light intensity distribution as shown in FIG. In (d), the light intensity distribution of the unimodal beam 13 is shown by a two-dot chain line corresponding to the bimodal beam 12.

FIG. 3E shows two converging spots 12a and 12b of the bimodal beam 12 and the unimodal beam 1
3 shows a relative positional relationship with the single converging spot 13a, and shows two converging spots 1 of the bimodal beam 12.
2a, the interval P _D of 12b is to determine the width P _W of as described in FIGS. 1 and 2, to be formed pits 8. The two focused spots section 12a for comparison to (e), the beam diameter P _R of the focused spot portion 13a of the unimodal beam 13 shown in correspondence to 12b, the laser beam having a wavelength λ and lens aperture It is set to the minimum value determined by the degree NA. The diameter P of this condensing spot 13a
_R and two focused spots section 12a, as is apparent from the comparison between the distance P _D of 12b, the beam diameter P _R is determined by the wavelength λ and lens numerical aperture NA, there is a limit in reducing whereas, the two focused spots 12a of the bimodal beam 12, the distance P _D of 12b, by passing the optional super-resolution filter 28A to 28C, is smaller than the beam diameter P _R of the minimum value be able to.

In the optical disk master exposure apparatus shown in FIG. 3, the first light modulator 27 of the bimodal beam system 22 always transmits a light beam at a constant light intensity regardless of information to be recorded. . Thus, the photoresist layer 2 on the glass substrate 1, the unexposed portions of the narrow width corresponding to the distance P _D of two focused spots portions 12a, 12b of the bimodal beam 12 is gradually formed constantly. The unexposed portion of the photoresist layer 2 is condensed by the objective lens 34 with a light beam whose light intensity is temporally modulated according to the information to be recorded by the second light modulator 30 in the unimodal beam system 23. since then in condensing spot portion 13a of the unimodal beam 13 formed by gradually exposed, the aforementioned unexposed portion of the photoresist layer 2, a width corresponding to the distance P _D of two focused spots portions 12a, 12b P A row of _W pits 8 is formed.

FIG. 5 is a process chart showing a method of manufacturing an optical disc master according to the second embodiment of the present invention in the order of steps. First, in a photoresist coating step shown in FIG. 3A, a photoresist is spin-coated on a glass substrate 1 having sufficient flatness and cleanliness to form a photoresist layer 2. Next, as shown in (b), a water-soluble photobleachable material having photobleachability is spin-coated on the surface of the photoresist layer 2 to form a photobleachable film 38. As the photobleachable material, for example, the exposure wavelength is 36
In the case of 4 nm, a material having photobleaching property at a wavelength around 364 nm is used. That is, the photobleachable film 38
Is formed by selecting a photobleachable material whose refractive index at the exposure wavelength matches the resist material of the photoresist layer 2 and applying the photobleachable material. Specifically, as a photobleachable material, for example, ACEM manufactured by Shin-Etsu Chemical Co., Ltd.
It is preferable to use -364iM (product registration name).

Subsequently, in the exposure step (c), the unimodal beam 13 light-modulated based on the recording signal corresponding to the information to be recorded is modulated to a constant light intensity regardless of the information to be recorded. The photoresist layer 2 is subjected to multiple exposure with the bimodal beam 12 through the photobleachable film 38. Here, the photobleachable film 38 and the photoresist layer 2 are
As described above, the exposure wavelength of the argon laser is 364 n
Since the photobleachable material and the resist material whose refractive indices are substantially equal to each other at wavelengths near m are selected and formed, multiple reflection at the interface between the photobleachable film 38 and the photoresist layer 2 during exposure is prevented. Can be deterred.

In (c), the state where there is no exposure by the unimodal beam 13, that is, the state where there is a signal for forming the pit 8 is on the left side, and the state where there is exposure by the monomodal beam 13, that is, the signal for forming the pit 8 is The absence of each is shown on the right side. Therefore, the two converging spots 1 of the bimodal beam 12 are provided on the left track of the photoresist layer 2.
A latent image 15 is formed between the exposed portions 2a and 12b, and a single focused spot portion 13a of the unimodal beam 13 and a bimodal beam 12 are formed on the right track of the photoresist layer 2. The whole of the width direction is exposed by the two condensing spot portions 12a and 12b, and the latent image 15 is not formed. Here, the photobleachable film 38 is formed on the photoresist layer 2.
Through the two focused spots 12 of the bimodal beam 12
Exposure at a and 12b makes it possible to form a fine latent image 15 by the contrast expansion effect of the photobleachable film 38. Details of this exposure step will be described later with reference to FIG.

Next, as shown in FIG. 5D, the water-soluble photobleachable film 38 is removed by washing with pure water. Subsequently, as the photoresist layer 2 is developed, the exposed portions of the positive type photoresist layer 2 are removed with a developing solution as shown in FIG. The pit 8 is formed with the image 15 remaining. As described above, the photoresist layer 2 has a condensed spot portion 13 of the unimodal beam 13 whose contrast has been enhanced by the contrast expansion effect of the photobleachable film 38.
Since the exposure is carried out at a, the end side wall is removed more perpendicularly to the glass substrate 1 during development. This makes it possible to form pits 8 in the photoresist layer 2 in which the pit length _Pl is further reduced.

When the photoresist layer 2 having the pits 8 formed thereon is dried and fixed on the glass substrate 1, an optical disk master 7 having a row of pits 8 for each track is completed. The pits 8 formed on the optical disk master 7 are
Since the edge is less tapered due to the contrast expansion effect of the photobleachable film 38, the optical disk manufactured using the optical disk master 7 has a significantly improved disk signal quality. The area shown by the two-dot chain line in (e) is an exposure area when eight rows of pits of adjacent tracks are formed in the same manner as described above, although not shown in (c). 8 is not formed.

In this embodiment, as described above, the photobleachable film 38 and the photoresist layer 2 are formed by selecting a photobleachable material and a resist material whose refractive indices at the exposure wavelength are substantially equal to each other. By doing so, multiple reflections at the interface between the photobleachable film 38 and the photoresist layer 2 during exposure are suppressed, so that the pits 8 formed afterimages on the photoresist layer 2 after development have rough surfaces. No surface is obtained. As a result, the quality of the disc reproduction signal does not decrease in the optical disc manufactured through the next process.

FIGS. 6A and 6B are explanatory views showing a state in which the bimodal beam 12 and the unimodal beam 13 are subjected to multiple exposure in the exposure step of FIG. 5C, wherein FIG. 6A is a schematic longitudinal section, and FIG. Each plane is shown. As in the first embodiment,
Two focused spots 12 in bimodal beam 12
The portion between a and 12b has an extremely low exposure intensity at which the resolution of the photoresist layer 2 is not possible.
Is not exposed between the two condensing spot portions 12a and 12b. On the other hand, the focused spot 13a of the unimodal beam 13 is positioned such that the center forms an image relative to the center between the two focused spots 12a and 12b in the bimodal beam 12, This focusing spot 1
3a exposes an unexposed portion between the two condensed spot portions 12a and 12b in the photoresist layer 2.

FIG. 6B shows two condensed spot portions 12 a and 12 b of the bimodal beam 12 and the unimodal beam 13.
Photoresist layer 2 formed by one condensing spot 13a
, And the respective portions exposed by the bimodal beam 12 and the unimodal beam 13 are indicated by oblique lines having different directions. Regardless of the information to be recorded, the bimodal beam 12 is moved while always keeping the photoresist layer 2 exposed at the two focused spots 12a and 12b. That is, the bimodal beam 12 is moved with respect to the photoresist layer 2 while leaving an unexposed portion having a small width P _D between the condensed spot portions 12a and 12b. On the other hand, the unimodal beam 13 is moved while the light intensity is modulated with time according to the information to be recorded, while exposing the unexposed portion remaining on the photoresist layer 2 by the condensing spot portion 13a. You.

Therefore, in this embodiment, as in the first embodiment, each of the condensed light spots 12a, 12b, and 13a in the positive photoresist layer 2 has a pit where an unexposed portion is to be formed. 8, the width P _{W of the} pit 8 to be formed is determined by the distance P _D between the two converging spots 12a and 12b of the bimodal beam 12. On the other hand, the pit length P _L is determined by the unexposed time due to the modulation of the light intensity of the unimodal beam 13. In this embodiment, the light intensity of the unimodal beam 13 is controlled by the photobleaching film 38. since the contrast enhancement, pit length P _L, it is possible to set shorter than that in the first embodiment without the photobleachable film 38. Further, the pits 8 formed according to the second embodiment have little taper at the edges, so that the quality of a disc signal is remarkably improved when the pit 8 is used as an optical disc.

Condensing spot 13a of unimodal beam 13
Is an existing beam shape having a minimum spot diameter determined by the wavelength λ of the laser and the lens aperture NA.
The width of the unexposed portion of the photoresist layer 2 to be exposed by the light beam has two converging spot portions 12a and 12a of the bimodal beam 12.
b is determined by a distance P _D, the further distance P _D of two focused spots portions 12a, 12b, the wavelength λ and of the laser that is the limiting conditions for setting a small exposure beam diameter of the laser beam L Since it can be set independently of the aperture NA of the condenser lens 3, it can be made smaller than the conventional minimum exposure beam diameter of the laser beam L. That is, in this exposure step, the wavelength λ of the laser
In addition, a latent image 15 capable of forming a pit 8 having a fine width _PW exceeding the limit of the aperture NA of the condenser lens 3 can be formed.

In the case where the tracks adjacent to the tracks on which the eight pit rows have been formed are sequentially exposed to form the eight pit rows, the same procedure as described with reference to FIG. 2 is performed. That is, after the exposure of the eight rows of pits to the n-th track is completed, when exposing the eight rows of pits to the (n + 1) -th track adjacent to the n-th track, one of the converging spot portions 12a of the bimodal beam 12 is exposed. Is set so as to overlap the exposed area 14 of the convergent spot 12b of the bimodal beam 12 during the exposure of the n-th track. Thereby, it is possible to prevent the photoresist layer 2 from being left unexposed at locations other than the locations where the pits 8 are formed. Also, the track pitch is the converging spot portion 12a of the bimodal beam 12,
12b with those same fine and diameter, to ensure greater than the width P _W of the pit 8 for determining an interval P _D of two focused spots portions 12a, 12b of the bimodal beam 12 Can be.

FIG. 7 is a block diagram showing an optical disk master exposing apparatus embodying an exposure step in the method for manufacturing an optical disk master according to the second embodiment. In FIG. Are given the same reference numerals. This optical disk master exposure apparatus is shown in FIG.
The only difference from the above device is the configuration in which the photobleachable film 38 is formed on the surface of the photoresist layer 2.

Therefore, this optical disk master exposure apparatus operates almost in the same manner as the apparatus shown in FIG.
The first light modulator 27 always sets the light beam at a constant light intensity and transmits the light beam regardless of the information to be recorded, so that the photobleachable film 38 is formed on the photoresist layer 2 on the glass substrate 1. unexposed portions of the narrow width equivalent is gradually formed constantly bimodal two focused spots portion 12a of the beam 12, 12b interval P _D via the. This photoresist layer 2
The unexposed portion is formed by condensing a light beam whose light intensity is temporally modulated in accordance with the information to be recorded by the second light modulator 30 of the unimodal beam system 23 by the objective lens 34. since Minesei gradually exposed with focused spot portion 13a of the beam 13, the above-mentioned unexposed portion of the photoresist layer 2, the width P _W corresponding to the interval P _D of two focused spots portions 12a, 12b pit 8 Are formed.

[0054]

As described above, according to the method for manufacturing an optical disk master of the present invention, in the exposure step, the width of the pit is controlled by the distance between the two condensed spots and the information to be recorded. Since a plurality of light beams including at least a light beam having a modulated light intensity are subjected to multiple exposure on the photoresist layer, the width of the pits for information recording is set by the distance between the two condensed spot portions while the photoresist layer is formed. The distance between the two focused spots can be set independently of the laser wavelength and the aperture of the focusing lens, which are the limiting conditions when setting the exposure beam diameter of the laser beam small. It is possible to make the diameter smaller than the minimum exposure beam diameter of the conventional laser beam. Therefore, in the exposure process, a latent image capable of forming a pit having a fine width exceeding the limit due to the laser wavelength and the aperture of the condenser lens can be formed in the photoresist layer, so that information can be further densified. Can be recorded.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which a photoresist layer is subjected to multiple exposure with a bimodal beam and a monomodal beam in an exposure step in a method for manufacturing an optical disc master according to a first embodiment of the present invention, and FIG. A schematic longitudinal section, (b) shows a schematic plane, respectively.

FIG. 2 is an explanatory diagram showing a positioning state of a bimodal beam when forming each pit row of adjacent tracks adjacent to each other in the same exposure step.

FIG. 3 is a block diagram showing an optical disk master exposure apparatus embodying the same exposure step.

4 (a) to 4 (c) are explanatory diagrams showing types of super-resolution filters in the optical disk master exposure apparatus, and FIG. 4 (d) is a diagram of a bimodal beam obtained by the super-resolution filters and the objective lens. FIG. 4E is an explanatory diagram showing a relative positional relationship between two converging spots of a bimodal beam and a converging spot of a unimodal beam.

FIGS. 5A to 5E are process diagrams showing a method of manufacturing an optical disc master according to a second embodiment of the present invention in the order of processes.

FIGS. 6A and 6B are explanatory views showing a state in which the photoresist layer is subjected to multiple exposure with a bimodal beam and a unimodal beam in the same exposure step, wherein FIG. 6A shows a schematic longitudinal section, and FIG.

FIG. 7 is a block diagram showing an optical disk master exposure apparatus embodying the same exposure step.

FIGS. 8A to 8F are process diagrams showing a general method of manufacturing an optical disc master.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glass substrate (substrate) 2 Photoresist layer 8 Pit 12 Bimodal beam 12a, 12b Condensing spot part of bimodal beam 13 Unimodal beam 13a Condensing spot part of unimodal beam 15 Latent image 28, 28A- 28C Super Resolution Filter 34 Objective Lens (Lens) 38 Photobleachable Film P _W Pit Width

Continuation of the front page F term (reference) 2H097 AA03 AA13 CA17 5D119 AA22 BA01 BB09 DA01 EB14 JA63 5D121 BB02 BB04 BB26 BB38

Claims (7)

[Claims] A step of applying a photoresist on the surface of a substrate to form a photoresist layer, and exposing the surface of the photoresist layer with a light beam whose light intensity is modulated with time according to information to be recorded. An exposure step of recording information as a latent image on the photoresist layer, and a developing step of developing the photoresist to form a pit row corresponding to the recorded information on the substrate, wherein the exposing step comprises: Multiple exposure is performed on a plurality of light beams including at least a light beam that regulates the width of a pit by an interval between two focused spot portions and a light beam whose light intensity is modulated based on information to be recorded. A method for manufacturing a master optical disc. 2. A bimodal beam having two converging spots for determining a pit width, and a single peak having a single converging spot and having a light intensity modulated based on information to be recorded. 2. The method according to claim 1, wherein the photoresist layer is exposed using a neutral beam. 3. The optical disk master according to claim 2, wherein the bimodal beam is obtained by condensing a light beam whose phase and amplitude are variably controlled by passing through a super-resolution filter by a lens. Production method. 4. A light intensity that cannot expose the photoresist layer between two converging spots of the bimodal beam,
The unimodal beam is focused on the photoresist layer such that the center of the focused spot is located at the center between the two focused spots of the bimodal beam. 4. The method of manufacturing an optical disk master according to claim 2, wherein 5. When forming a pit row of each of a plurality of tracks adjacent to each other, one of the converging spot portions of the bimodal beam has been exposed at the time of exposing a track in a front row of two tracks adjacent to each other. 5. The method of manufacturing an optical disc master according to claim 2, wherein an exposure area of the other converging spot portion of the bimodal beam is overlapped and exposed to a region of the second row when exposing a track in a rear row. Method. 6. A photobleachable film is formed on a surface of a photoresist layer, and the photoresist layer is subjected to multiple exposure with a plurality of light beams through the photobleachable film.
The method for manufacturing an optical disk master according to any one of the above. 7. The method of manufacturing an optical disk master according to claim 6, wherein the photoresist layer and the photobleachable film are formed of materials having the same refractive index at the exposure wavelength.