JP2001325752A - Method for manufacturing stamper for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical disk stamper by which fine grooves and pits having a smaller width than the beam diameter of the exposure light spot can be formed with good accuracy. SOLUTION: In the process for manufacturing a stamper for an optical information recording medium including a process of applying a photoresist on a glass substrate, a resist mask method to etch a lower layer by using the photoresist layer as a mask layer is used, and moreover, the exposure beam spot 10 is converged by the super resolution effect by a cross light-shielding mask 5. In this way, a groove or pit having a smaller width than the beam diameter of the exposure light spot can be formed in the lower layer.

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 stamper for an optical information recording medium, and more particularly to a method for accurately forming grooves and pits smaller than the beam diameter of an exposure spot. Thus, the present invention is also effective when applied to a fine pattern forming method in a semiconductor process.

[0002]

2. Description of the Related Art On a master disk for an optical disk, guide grooves for tracking and pits having concavities and convexities representing address data are formed in advance in a spiral shape or concentric circles. Such a guide groove or pit pattern is formed by forming a photoresist layer on a glass substrate serving as a master, converging a light beam whose intensity is modulated according to a pattern to be formed by an objective lens of a master exposure apparatus, and forming a photo-resist. It is obtained by exposing the resist layer and then developing it. Generally, in a photoresist, a latent image is formed by a photo-crosslinking reaction and a thermal cross-linking reaction due to exposure. Therefore, the groove width of the opening is about 10% to 20% of the beam spot diameter (the long side of the trapezoidal shape: Wtop) becomes wider. Further, since the light intensity distribution of the focused beam is a Gaussian distribution, the groove formed in the photoresist has a trapezoidal shape (see development in FIG. 1D). The problem with the trapezoidal groove is that when the track pitch becomes narrower, the opening of the groove interferes between adjacent tracks, the height of the flat part (land) between the grooves decreases, and the depth of the groove The point is that it cannot be controlled by the thickness of the resist. In addition, there is a problem that the recording characteristics of an optical information recording medium manufactured from a stamper whose lands are not flat are deteriorated (a crosstalk signal from an adjacent track increases,
In particular, the jitter characteristic is reduced). For this reason, a large-capacity optical information recording medium stamper with a narrow track pitch needs to have a narrow groove width and a rectangular cross section. In order to narrow the groove formed in the photoresist, the wavelength of the exposure beam may be shortened and the numerical aperture NA of the objective lens may be increased. However, the depth of focus at the time of exposure is reduced, so that the groove shape may fluctuate. I am concerned. Therefore, a photolithography technique is required that can obtain a thin groove cross section smaller than the exposure beam spot without using a short wavelength and a high NA. As a conventional technique that enables formation of a groove having a diameter equal to or smaller than the exposure beam spot diameter, a method of etching a lower layer using a resist mask pattern of an upper layer is known as a resist mask method. There is known a method of narrowing a light beam to a diffraction limit of an objective lens or less.
Examples thereof are described in JP-A-6-215408 and JP-A-10-255308. In the above, a circular or striped super-resolution mask is installed so as to be perpendicular to the beam. The above-mentioned laser beam is divided into two, and a super-resolution optical system and a π phase shift are used to obtain an interference effect. To obtain a small spot below the diffraction limit.

[0003]

2. Description of the Related Art When the super-resolution effect is used, the main beam can be made finer, but side lobes are generated around the main lobe according to the shape of the super-resolution mask. For example, in the case of a rectangular mask, side lobes are generated on the left and right sides of the main lobe, and in the case of a circular mask, side lobes are generated in a circle surrounding the main lobe. In the case of the cross light-shielding mask used in the present invention, side lobes are generated at four locations above, below, left, and right of the main lobe (see FIG. 3). As the track pitch becomes narrower, this side lobe is applied to adjacent tracks during photoresist exposure,
Light exceeding the amount of light originally required at the time of exposure is integrated by the side lobes, which means overexposure (FIG. 5).
(A)). In this case, the width of the groove or pit becomes larger than expected, the width of the land becomes inconsistent, or the flatness is lost, and the recording characteristics of the optical information recording medium manufactured from this stamper deteriorate. The problem described above occurs. In the method disclosed in Japanese Patent Application Laid-Open No. Hei 6-215408, the above problem occurs due to the generated side lobes regardless of whether a circular light-shielding mask or a stripe-shaped light-shielding mask is used. JP-A-10-25
In Japanese Patent No. 5308, the beam can be narrowed down by using the super-resolution effect and the interference effect, but the side lobe cannot be completely eliminated. In addition, since the optical system is divided into two and an optical modulator is installed in each,
Another drawback is that the exposure optical system becomes very expensive.

[0004]

An object (1) of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for accurately forming grooves and pits smaller than the beam diameter of an exposure spot. (Problem of the invention according to claim 1) Further, the problem (2) is to specify a loss rate of a light beam by a cross light shielding mask and to provide a range in which light intensity is not insufficient (according to claim 2). The problem (3) is to provide a method that does not result in overexposure during groove and pit exposure (the problem of the invention according to claims 3 and 4). An object of the present invention is to reduce an operation for adjusting an optical system and to prevent an accident (an object of the invention according to claim 5).

[0005]

[Measures taken to solve the problem] Means for Solving Problem (1) Means (1) taken to solve the above problem (1) are:
A step of applying a photoresist on a glass substrate, a step of heat-treating the photoresist layer, a step of condensing a light beam by an objective lens and exposing a predetermined groove pattern on the photoresist layer, Developing, washing, and drying the completed photoresist layer to produce a glass master having a predetermined groove pattern, forming a conductive film on the surface of the glass master, and electroforming the conductive film with nickel. An optical information recording medium comprising a step of producing a nickel plate having a groove pattern in which concavities and convexities are inverted with respect to a resist groove pattern, and steps of peeling, removing photoresist, washing, polishing the back surface, and processing inner and outer diameters of the nickel plate. In the stamper manufacturing process, a water-soluble resin layer that does not react by exposure between the glass master and the photoresist layer (hereinafter referred to as “lower layer”). ), The thickness of the lower layer is the same as the groove depth formed on the surface of the stamper, a fine pattern is formed on the photoresist layer by exposure to a master, and the lower layer is etched by using the photoresist layer as a mask. When a fine pattern is formed, and then the photoresist layer is removed to produce a glass master having the fine pattern,
The material of the lower layer is a water-soluble resin resin selected from polyvinyl alcohol, methylcellulose, or polyvinylpyrrolidone. As a means for etching the lower layer, when forming a fine pattern on the photoresist layer by wet development, the alkaline development In a method of manufacturing a stamper for an optical disc, comprising a step of removing a photoresist layer after simultaneously etching a lower layer in a step of washing with liquid or pure water after development, the light beam has a cross-shaped light shielding portion The narrowing is performed by using the super-resolution effect of a light-shielding mask (hereinafter, this is referred to as a “cross-shaped light-shielding mask”).

[0006] 2. Means for Solving Problem (2) Means taken to solve the above problem (2)
According to the invention, the loss rate of the light beam due to the cross light shielding mask of the above means (1) is set to less than 60% of the entire light amount.

[0007] 3. Means for Solving Problem (3) Means taken to solve the above problem (3)
The present invention according to (4) is that the cross-shielding mask of (1) is capable of rotating around the traveling direction of the light beam. ) Means that the rotation angle of the cross light-shielding mask of the means (1) is in the range of 0 ° to 45 °.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. The steps from the master to the stamper fabrication according to the present invention are as shown in FIG. 1, and the respective steps are as follows. (1) Substrate cleaning In order to remove dust adhering to the substrate with ultrapure water,
Wash and dry (not shown in FIG. 1). (2) Surface Treatment In order to improve the applicability of the water-soluble resin layer to the glass substrate, organic substances on the surface of the glass substrate are removed by an ozone treatment and an oxide film is formed on the surface. By this effect, the wettability of the water-soluble resin on the glass substrate is improved, the thickness of the water-soluble resin can be made uniform, and the adhesion between the water-soluble resin and the glass substrate is strengthened (not shown in FIG. 1). (3) Coating of lower layer A water-soluble resin is spin-coated on the surface-treated glass substrate, and is dried by heating and cooling. At this time, it is necessary to apply the lower layer having the same thickness as the depth of the groove formed on the surface of the stamper (see formation of the lower layer in FIG. 1A). (4) Pretreatment After forming the lower layer in the step of applying the lower layer, HMDS (hexamethyldisilazane) is spin-coated for the purpose of increasing the adhesion between the lower layer and the photoresist, and dried at high speed ( (Not shown in FIG. 1). (5) Mask Layer Application A photoresist is spin-coated on the surface that has been subjected to the HMDS treatment in the pretreatment step, and is heated, dried, and cooled to form a mask layer (see FIG. 1B). See figure). (6) Master exposure The master manufactured in the above-mentioned mask layer coating step is subjected to master exposure with a Kr gas laser. The master exposure will be described later in detail. By exposing the master while rotating and traversing the master, a spiral latent image is formed on the mask layer of the photoresist film. (Refer to the master exposure drawing in FIG. 1C). (7) Development / Rinse The exposed master is developed, the exposed portion (the portion where the latent image is formed) is removed, rinsed with pure water, and rotated and dried (see the development diagram of FIG. 1D). reference). At this time, the photoresist film functions as a mask layer at the time of development, and the lower water-soluble resin layer is etched with a developer and a rinse.
The width of the groove formed in the lower layer is determined by the width (Wbot) of the bottom of the trapezoidal shape of the mask layer (see the development diagram in FIG. 1E). (8) Mask layer removal The mask layer (photoresist film) is removed with a stripping solution,
After substitution with a solvent, the substrate is dried. For this solvent, it is necessary to select a solvent that does not dissolve the lower layer (water-soluble resin layer) (see the drawing of the mask layer removal in FIG. 1F). (9) Conductive film treatment After the mask layer is removed in the mask layer removing step,
A nickel film is formed by sputtering on the surface of the master having the groove pattern (see the diagram of the conductive film treatment in FIG. 1 (g)). (10) Nickel electroforming A master with a conductive film that has been subjected to the conductive film processing in the above-described conductive film processing step is subjected to nickel electroforming, and nickel is laminated (FIG. 1).
(Refer to the figure of nickel electroforming in (h)). (11) Stamping The nickel electroformed plate is peeled off from the glass master,
Polish the back surface (the surface on which the groove pattern is not formed), wash the lower layer film (water-soluble resin film) remaining on the groove pattern surface with pure water, dry at high speed, and press the inner and outer diameters to desired dimensions. The stamper is completed by processing (see the drawing of peeling, polishing, cleaning, and inner and outer diameter processing in FIG. 1 (i)).

A feature of the manufacturing process of the present invention is that a water-soluble resin layer is provided between a glass substrate and a photoresist layer. The groove pattern formed in the photoresist film is used as a mask layer, and is formed by etching. The lower groove pattern is formed on the stamper. As a result, the bottom width of the groove becomes the groove width of the lower layer, so that a groove that is narrower than the groove cross section formed in the photoresist film can be formed in the lower layer. Can be obtained.
In addition, since a Kr gas laser having a wavelength of about 400 nm is used as an exposure light source, an optical system not in an expensive ultraviolet region but in a normal visible region can be used, which is very advantageous in cost. However, the above method alone has a limit when the track pitch is narrowed to further increase the capacity of the optical disk. Therefore, in the present invention, the super-resolution effect that can further narrow down the light beam itself is used. FIG. 2 is a schematic view of an exposure optical system according to the present invention.

The light intensity of the light emitted from the Kr gas laser 1 is stabilized by the stabilizer 2. Next, in the case of a pit,
The modulator 3 is actuated by a signal pulse corresponding to the pit length, and the light is turned on and off to cope with it. In the case of a groove, a wobble is applied by the deflector 4. Next, the light narrowed down by the cross light shielding mask 5 installed perpendicularly to the traveling direction of the light is exposed on the master 7 by reduction projection with the objective lens 6. Due to the super-resolution effect of the cross light-shielding mask 6, the intensity distribution of the projected spot of light becomes narrower and sharper than the normal Gaussian distribution (see FIG. 3B). The loss rate of the amount of light shielded by the cross light shielding mask 6 is set to be less than 60% of the entire light beam. By defining in this way, it is possible to prevent the light intensity from becoming insufficient at the time of exposing the master. Since the master 7 is moved linearly by the slider 9 while rotating on the turntable 8, grooves or pits can be drawn spirally or concentrically.

However, what matters here is the side lobe. In other words, as the capacity increases, the track pitch also becomes narrower, but with this, the side lobe 12 of the beam spot 10 due to the super-resolution effect is just over the position of the adjacent track (see FIG. 6A). It becomes like this. When the side lobes 12 are applied in this manner, the light amount of the side lobes 12 is accumulated in the adjacent track, and the state becomes the same as that of the overexposure. As a result, the lateral width of the latent image formed in the photoresist increases accordingly, and the width of the grooves and pits formed in the photoresist increases as compared with the case where the photoresist is exposed with the original light amount. When the width of the land is not constant, or when it is severe, the land itself may be broken, resulting in a problem that the signal characteristics are greatly reduced. Therefore, the cross light shielding mask 5 is rotated about the traveling direction of the light beam. When the cross-shielding mask 5 rotates, the beam spot also rotates along with the rotation, and the position of the side lobe 12 also moves along the circumference of the main lobe 11 (FIGS. 4A, 4B and 5A). ), (B)). By doing so, the side lobe 12 is not placed on the position of the adjacent track,
Overexposure does not occur (see FIG. 6B). In this case, as described above, since the side lobes 12 are formed at four positions on the upper, lower, left, and right sides of the main lobe 11, the beam spot has the maximum width (Wmax) when the light shielding mask is in the cross state (0 °). That's 45
° The minimum width (Wmi
n) (see FIGS. 4A and 4B). From this, it can be seen that the range in which the cross light shielding mask 5 is rotated should be 0 ° to 45 °.

In order to rotate the cross light shielding mask 5, a remote control method using a motor 21 is used. The type of the motor 21 to be used is not particularly limited, as long as it can perform almost accurate positioning by a command, such as a stepping motor or a servomotor. The beam spot is measured in advance on a monitor by an image sensor or the like, and the rotation angle of the cross-shading light-shielding mask 5 with no side lobe applied is calculated in accordance with the track pitch. 23, the driver 23
By driving the motor 21 in response to a signal from the camera, the cross light shielding mask 5 can be rotated by a required angle (see FIG. 7). Of course, it is also possible to move the cross-shielding mask directly by hand, but in this case, the laser light enters the eyes during the work, which may cause blindness, so the worker must wear safety glasses or use a shutter, etc. It is absolutely necessary to block the laser light at the time. Further, if the optical system is shifted by accidentally touching other parts during the operation, it takes a lot of trouble to correct the optical system. By performing the remote operation as shown in FIG. 7, the danger in the manual operation is eliminated. By adopting the above method, a groove or a pit having a width equal to or less than the diffraction limit of the light beam can be easily, simply and safely formed.

[0013]

The effects of the present invention are clear from the above description. The points of descent of the invention for each claimed invention are as follows. 1. Advantageous Effects of the Invention According to the present invention, a resist mask method of etching a lower layer using a photoresist layer as a mask layer is used, and the exposure beam spot is narrowed by a super-resolution effect using a cross-shaped light shielding mask. Finer grooves or pits can be formed in the lower layer.

2. Effect of the Invention According to Claim 2 By setting the loss ratio of the exposure beam by the cross light shielding mask to less than 60 %%, it is possible to secure a necessary light amount at the time of exposure and prevent light intensity shortage.

[0015] 3. According to the third aspect of the present invention, since the cross-shaped light shielding mask can be rotated around the traveling direction of the light beam, the position of the side lobe of the beam spot can be moved to a position such that it does not cover an adjacent track. It is possible to prevent the width of the groove or the pit from being increased due to oversizing.

4. According to the fourth aspect of the present invention, since the rotation angle of the rotation of the cross light shielding mask is in the range of 0 ° to 45 °, it is possible to cover the entire width of the beam spot from the maximum value to the minimum value.

5. Advantageous Effects of Invention According to the fifth aspect, since the cross-shaped light-shielding mask is rotated by using a remote operation driven by a motor, there is no need for a worker to directly look into the optical system and work, thereby greatly reducing danger and labor. Can be.

[Brief description of the drawings]

FIG. 1 is a process flow chart from master production to stamper production according to the present invention.

FIG. 2 is a schematic diagram of an optical system for exposing a master in a master manufacturing process of FIG.

3A is a schematic diagram showing a relationship between a cross light shielding mask and an objective lens incident beam in the master disk exposure optical system of FIG. 2, and FIG. 3B is a super-resolution beam created by the cross light shielding mask; FIG. 3 is a schematic diagram showing a spot shape and a light intensity distribution of a super-resolution beam spot.

FIG. 4A is a schematic diagram illustrating a rotation state of a cross light shielding mask, and FIG. 4B is a schematic diagram illustrating a relationship between rotation of the cross light shielding mask and a change in a width of a beam spot shape.

5A is a perspective view showing the shape of a beam spot on the master when the inclination of the cross-shielding mask is zero (the rotation position is ten positions), and FIG. FIG. 9 is a perspective view showing the shape of a beam spot on the master at the time of ° (the rotation position is the X position).

6 (a) is a plan view showing a pit exposure state in FIG. 5 (a), and FIG. 6 (b) is a plan view showing a pit exposure state in FIG. 5 (b).

FIG. 7 is a schematic view of a rotation driving system of a cross light shielding mask.

[Explanation of symbols]

 1: Kr gas laser 2: stabilizer 3: modulator 4: deflector 5: cross light shielding mask 6: objective lens 7: master 8: turntable 9: slider 10: beam spot 11: main beam 12: side lobe 21: motor 22 : Controller 23: Driver

Claims (5)

[Claims] 1. A step of applying a photoresist on a glass substrate, a step of heat-treating the photoresist layer, and a step of exposing a predetermined groove pattern on the photoresist layer by condensing a light beam by an objective lens. Developing a glass master having a predetermined groove pattern by developing, washing, and drying the exposed photoresist layer; forming a conductive film on the surface of the glass master; It is composed of a step of preparing a nickel plate having a groove pattern in which the groove pattern of the photoresist is inverted with respect to the groove pattern of the photoresist, and a step of peeling, removing the photoresist, cleaning, polishing the back surface, and processing the inner and outer diameters of the nickel plate. In the process of manufacturing a stamper for an optical information recording medium, a water-soluble resin layer (hereinafter referred to as a lower layer) which does not react by exposure between a glass master and a photoresist layer. The thickness of the lower layer is the same as the depth of the groove formed on the surface of the stamper, a fine pattern is formed on the photoresist layer by master exposure, and the lower layer is etched using the photoresist layer as a mask to form the lower layer. When forming a fine pattern, and then removing the photoresist layer to produce a glass master having a fine pattern, the material of the lower layer is a water-soluble resin resin selected from polyvinyl alcohol, methyl cellulose, or polyvinylpyrrolidone, As a means for etching the lower layer, when a fine pattern is formed on the photoresist layer by wet development, in the step of washing with an alkaline developer or pure water after development, the lower layer is etched at the same time. The method of manufacturing a stamper for an optical disc, comprising: Method of manufacturing a stamper for optical disc and a light beam is narrowed by utilizing the super-resolution effect by the light shielding mask (described as hereafter cross shading mask) having a cross-shaped light shielding portion. 2. The method for manufacturing a stamper for an optical disk according to claim 1, wherein a loss rate of the light beam by the cross light shielding mask is less than 60% of the entire light amount. 3. The method of manufacturing a stamper for an optical disk according to claim 1, wherein the cross-shielding mask can be rotated about the traveling direction of the light beam. 4. The rotation angle of the cross light-shielding mask is 0 ° to 45 °.
2. The method of manufacturing a stamper for an optical disk according to claim 1, wherein the range is defined as ゜. 5. A means for rotating a cross-shaped light shielding mask,
2. The method for manufacturing an optical disk stamper according to claim 1, wherein remote control using motor driving is performed.