Patent Application
20060222967
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-92759 filed on Mar. 28, 2005 in Japan, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic disk medium of a discrete type, a reticle for projection exposure for manufacturing an original disk serving as a mold for a stamper used during manufacture of the magnetic disk medium, and a method for manufacturing a magnetic disk medium using the reticle.
2. Related Art
In a technical trend to density growth of a hard disk (hereinafter, also called “magnetic disk”), a medium structure of the so-called discrete type where magnetic portion regions generating magnetic signals are partitioned by non-magnetic regions has been proposed. For example, JP-A-2004-110896 describes a recording/reproducing system of a medium of a discrete type having a data zone and a servo zone. However, there is not a description about how to manufacture the medium of a discrete type in JP-A-2004-110896.
On the other hand, U.S. Pat. No. 5,772,905 describes a technique for transferring a mold pattern of 200 nm or less on a film, which is so-called “nano-imprint lithography”. JP-A-2003-157520 describes a technique for transferring a magnetic disk pattern of a discrete type utilizing imprinting. JP-A-2003-157520 also describes an example where a medium pattern is formed using a stamper obtained from an original disk manufactured utilizing an electron beam lithography, but it does not include a description about an approach of the electron beam lithography itself.
In general, a magnetic disk apparatus is provided inside thereof with a toroidal disk-like magnetic disc, a head slider including a magnetic head, a head suspension assembly supporting the head slider, a voice coil motor (VCM), and a circuit board.
The magnetic disk where ring-like concentric tracks are sectioned and each track has sectors sectioned for each predetermined angle is attached to a spindle motor to be rotated so that various digital data elements are recorded and reproduced by the head. Therefore, user data tracks are arranged in a circumferential direction, while servo marks for positional control are arranged so as to cross the respective tracks. The servo mark includes regions such as a preamble portion, an address portion, and a burst portion. Besides, the servo mark can include a gap portion.
It is desirable that both the user disk track region and the servo region are simultaneously formed in a stamper original disk for manufacturing a magnetic disk of a discrete type utilizing an imprint system. When one of both regions is added after the other is formed, it becomes difficult to position the one to the other, which results in requirement for a complicated step(s).
In manufacture of an original disk, its pattern can be formed by exposing photosensitive resin using a mercury lamp or actinic rays such as ultraviolet rays, electron beams, or X-rays. Especially, it is preferable that an approach of performing direct lithography using an electron beam synchronized with a signal source is utilized for forming a magnetic disk pattern which requires drawing concentric circles, because the electron beam can be deflected. For example, using an electron beam lithographing apparatus of a stage continuous moving system having a movement mechanism and a rotation mechanism based upon one direction moving shaft, a pattern can be formed by irradiating a spot beam from one point on the moving shaft to photosensitive resin on a substratee placed on a stage to perform electron beam exposure.
However, unless the electron beam is not applied with external force, a spiral pattern is drawn. In order to get a concentric circle deflection is applied on an electron beam while changing intensity of the electron beam for each rotation in the exposure step. On the other hand, lines in a radial direction can be drawn in a continuous manner by emitting a beam or stopping emission of a beam only when each line reaches a predetermined angle. Specifically, when a medium where the servo region and the data region have been arranged is obtained, a desired exposure pattern including connected lines can be obtained by applying such deflection as to increase a deflection amount linearly according to rotation of the stage for each rotation and make the deflection amount zero at a return time of the stage to its original position after one rotation. When positive type resist is used, an exposed portion constitutes a recessed portion after developed, and it becomes a projection portion after a stamper is manufactured by electroforming. The servo portion of the medium can be formed in an arc shape corresponding to a locus of an arm of the head portion instead of a constitution that the servo portion extends straightly in a radial direction.
Now, since the movement mechanism and the rotation mechanism based upon the one direction moving shaft include some feeding precision error or rotational jitter in fact during exposure, collapsing of a pattern occurs. As an approach for solving this problem, a reduced projection exposure can be used.
According to the reduced projection exposure, even if there is unevenness in a pattern, the size of the unevenness is reduced due to reduced projection. The reduced projection is performed by irradiating such a beam as an electron beam on a mask (hereinafter, called “reticle”) with a pattern opening to be projected, reducing a beam which has passed through the opening, and irradiating the reduced beam on a substrate to be exposed.
The electron beam reduced projection technique mainly includes SCALPEL (Scattering with Angular Limited in Projection Electron Lithography) system described in S. D. Berger et al., Applied Physics Letters, 57, 153 (1990) and PREVAIL (Projection Exposure with Variable Axis Immersion Lens) system disclosed in Japanese Patent No. 2829942. In these systems, a mask of a stencil type (hereinafter, also called “stencil mask”) and a mask of a membrane type (hereinafter, also called “membrane mask”) are used as masks.
When the stencil mask is used, an electron beam passes an opening of the stencil mask to scatter at a non-opening portion of the mask. The membrane mask is constituted of a membrane portion made from light element which allows easy transmission of an electron beam and a heavy metal pattern layer which is formed on the membrane to scatter an electron beam. A film such as silicon film or a silicon nitride film is used as the membrane portion, while chromium (Cr) or tungsten (W) is used as material for the pattern layer.
Since the opening of the stencil mask through which a beam passes is a through-hole, low scattering or chromatic aberration as caused in the membrane mask does not occurs. In view of a structure of the stencil mask, however, a mask having a pattern such as a toroidal pattern having an opening at the center thereof can not be produced due to opening for defining an outer periphery of the doughnut shape. Therefore, an approach of using a complementary mask to conduct plural exposures is applied to such an issue. However, such an approach includes a problem of positioning or throughput. A cantilever pattern may become weak in mechanical strength, which causes damage easily.
On the other hand, since the membrane mask is provided with the membrane portion, even such a pattern as a toroidal pattern can be formed. However, the membrane mask includes such a tendency that a toroidal pattern or a cantilever pattern is weak like the stencil mask. In the membrane mask, such a drawback arises that slight low scattering occurs at a time of transmission of an electron beam through the membrane, which results in occurrence of chromatic aberration.
Especially, in the stencil mask, a problem of strength arises in such a constitution that a large non-opening pattern is supported using a fine pattern wire. On the contrary, when there is a large opening pattern, a pattern portioned around the opening pattern can not obtain a sufficient support, which easily causes a problem similar to the problem occurring in the cantilever pattern. In the membrane mask, the problem of strength is relatively reduced, but such a problem arises that strain depending on a pattern easily occurs due to a difference in stress between the heavy metal and the light element thin film.
Here, since such a disk as a hard disk medium, a compact disk, and a DVD (digital versatile disk) is formed in a doughnut shape, a mask used to manufacture an original disk therefor must have a toroidal pattern necessarily. When a projection mask used to manufacture an original disk for such a doughnut type is prepared, a central portion of a doughnut pattern is generally formed in a non-opening pattern or an opening pattern, but such a mask includes such a problem that strength becomes weak, as described above.
The present invention has been made in view of these circumstances, and an object thereof is to provide a reticle which has a high strength even it is formed in a doughnut shape, a method for manufacturing a magnetic disk medium using the reticle, and a magnetic disk medium using the same.
A reticle according to a first aspect of the present invention includes a toroidal pattern, a pattern of a central portion of the toroidal pattern including an opening portion and a non-opening portion.
The pattern of the central portion can be formed in a fan shape, in a network defined with triangular holes, a network defined with tetragonal holes, or a network defined with regular hexagonal holes, or it is formed by a combination of these holes.
One of an alignment mark and an identification mark can be provided within the pattern of the central portion.
The reticle can be of a membrane type.
The reticle can be of a stencil type.
An opening area ratio of the central portion of the toroidal pattern can be an opening area ratio of the toroidal pattern or more.
An opening area ratio of the central portion of the toroidal pattern can be in a range of 50% or more to 98% or less.
The reticle can be used for electron beam reduced projection exposure.
A method for manufacturing a magnetic disk medium according to a second aspect of the present invention, which performs manufacturing of a magnetic disk medium using imprint process, includes: forming a master disk having a resist pattern formed on a surface of the master disk in order to manufacture a stamper used in the imprint process by conducting electron beam projection exposure using the above-described reticle.
A magnetic disk medium according to a third aspect of the present invention is manufactured according to the manufacturing method above-described.
Embodiments of the present invention will be explained below in detail with reference to the drawings.
Reticles of a first embodiment and a modification thereof according to the present invention will be explained. A reticle of the embodiment is used in a projection exposure apparatus. As shown in
As shown in
On the other hand, a toroidal pattern of the reticle 2 according to the embodiment is constituted such that a central portion 10 has wires (non-opening portions) 12 extending in a radial direction. That is, the embodiment is constituted such that the central portion 10 includes the non-opening portions 12 and an opening portion 14, which is different from the conventional toroidal patterns. In
If a pattern positioned in a central portion of a toroidal pattern is provided with the non-opening portions 12 and the opening portion 14 in this manner, as shown in
At all events, the reticle 2 is required to only have the non-opening portion 12 and the opening portion 14 in the pattern positioned at the central portion of the toroidal pattern, where it is preferable that the pattern at the central portion is formed to be symmetrical about a point.
An opening area ratio on the central portion of the toroidal pattern (=an area of an opening portion on the central portion/an area of the central portion) should be set to be at least an opening area ratio of the toroidal pattern (=an area of the opening portion of the whole pattern/an area of the whole pattern), and it is preferably set in a range of 50% or more to 98% or less. When the opening area ratio on the central portion of the toroidal pattern exceeds 98%, the toroidal pattern can not be supported sufficiently, so that the strength of the reticle 2 can not be made sufficiently high, as compared with that of a reticle with a cantilever pattern. On the other hand, when the opening area ratio on the central portion of the toroidal pattern is set to be less than 50%, especially, it is set to be at most the opening area ratio of the toroidal pattern, such a setting differs little from the non-opening state where it is difficult for the surrounding toroidal pattern portion about the central portion of the toroidal pattern to support the central portion, so that a possibility that a reticle with high strength can be obtained is reduced.
Such a pattern as shown in FIGS. 1 to 8 does not cause falling-off and it does not include a large cantilever portion, so that a reticle 2 with high strength can be obtained. Here, the reticle 2 may be of the stencil type or of the membrane type. However, when each of the patterns shown in FIGS. 6 to 8 is applied to the stencil type, falling-off is caused, so that these patterns should be applied to the membrane type.
Though a method for manufacturing a reticle is not limited to a specific one, it is preferable in view of saving the need for the positioning step that a sub-field commonly used is not included.
In the embodiment, a case that the number of sectors is four is shown for ease of explanation, but the number may exceed a hundred. A non-opening portion (not shown) between tracks in a radial direction is not required to be continuous and straight. However, it is preferable for eliminating unevenness of strength that the non-opening portion is disposed at intervals of a fixed range to some extent.
In FIGS. 1 to 8, outer frame portions of the respective rectiles are each shown to have a circular shape, but they are not formed in the circular shape necessarily. Each outer frame portion may be formed in a square shape. Incidentally, it is preferable for maintaining evenness of strength that the outer frame portion has a shape approximating to a circle concentric with the pattern or an outer frame of the reticle has a width relative to the pattern of the reticle to such an extent that evenness of strength can be obtained.
In the embodiment, the size of the reticle, the size of the magnetic disk medium, and the size ratio therebetween are not limited to specific ones. However, when the size of the reticle is excessively large, such a problem as lack of strength or large-sizing of the apparatus itself occurs. When the reduction ratio is reduced, and the sizes of the reticle and the magnetic disk medium are not so changed, it becomes difficult to achieve reduction of unevenness of a pattern which is the advantage obtained using the reduced projection exposure. Therefore, for example, it is preferable that the size of the magnetic disk medium is 2 inches or less, the size of the reticle is 8 inches or less, and the reduction magnification is in a range of about ½ to ⅕.
The pattern of the reticle and the pattern of the magnetic disc medium are not required to be analogous to each other necessarily, and the pattern of the reticle may be a pattern making an allowance for optical compensation from exposure.
As explained above, according to the embodiment and the modification thereof, a reticle having high strength despite toroidal pattern can be obtained.
Next, a method for manufacturing a magnetic disk medium of a discrete type according to a second embodiment of the present invention will be explained With reference to
Photosensitive resin (hereinafter, called “resist”) 24 is applied on a substrate 22 (see
Thereafter, the resist 24 is developed using developing solution, and a resist pattern 24a is formed so that a resist original disk is manufactured (see
Next, an electrically conductive thin film 26 is formed on the resist pattern 24a of the resist original disk utilizing such process as Ni sputtering process (see
Next, the Ni film 28 is peeled off from the resist original disk constituted of the resist 24a and the substrate 22, so that a stamper 30 constituted of the electrically conductive film 26 and the Ni film is formed (see
Next, as shown in
Next, the resist 34 is etched using the pattern transferred on the resist 34 as a mask so that a resist pattern 34a is formed (see
Next, a protective film 36 is formed on a whole surface of the magnetic disk medium substrate 31 with the discrete magnetic layer 32a, so that a magnetic disk medium is completed (see
It is preferable in view of an approach applied to the manufacturing method according to the embodiment that the magnetic disk medium manufactured by the manufacturing method is formed in a disk-shape or in a doughnut shape, but a size of the magnetic disk medium is not limited to a specific one. However, it is preferable that the size is 3.5 inches or less such that a lithographing time utilizing an electron beam does not become excessive. It is preferable that the size is 2.5 inches or less such that a pressing force applied at an imprinting time does not become excessive. When reduced exposure projection is used, it is more preferable, especially, in view of mask productivity that the size is 1.0 inch or less, for example, 0.85 inch. In the magnetic disk medium, one side face or both side faces can be used as a recording face or recording faces.
A shape of the substrate on which a pattern is formed using the manufacturing method of the embodiment is not limited to a specific one, but it is preferably disk-shaped, for example, a silicon wafer disk can be used. Here, the disk may have a notch or an oriented flat. As another substrate, a glass substrate, an Al series alloy substrate, a ceramic substrate, a carbon substrate, a compound semiconductor substrate can be used. The glass substrate can be made from amorphous glass or crystal glass. As the amorphous glass, soda lime glass, aluminosilicate glass, or the like can be used. As the crystal glass, there is lithium series crystal glass. As the ceramic substrate, a sintered body mainly containing aluminum oxide, aluminum nitride, silicon nitride, or the like, or material obtained by fiber-reinforcing the sintered body, or the like can be used. As the compound semiconductor substrate, there are GaAs, AlGaAs, and the like.
The magnetic disk medium where ring-like concentric tacks are sectioned and each track has sectors sectioned for each predetermined angle is attached to a spindle motor to be rotated so that various digital data elements are recorded and reproduced by the head. Therefore, user data tracks are arranged in a circumferential direction, while servo marks for positional control are arranged so as to cross the respective tracks. The servo mark includes regions such as a preamble portion, an address portion which is written the information of tracks or sectors numbers, and a burst portion due to the relative position detection for the tracks. Besides, the servo mark can include a gap portion.
Examples of the present invention will be explained below.
A method for manufacturing a reticle according to Example 1 of the present invention will be explained with reference to
A membrane film 41 with a thickness of 0.1 μm made from diamond was formed on a silicon substrate 40 by plasma CVD (chemical vapor deposition) process, and a silicon oxide film 42 serving as a stopper at an etching time was formed thereon (see
Next, the substrate thus obtained was conveyed to a predetermined position inside an electron beam lithographing apparatus (not shown) using a conveying system (not shown) of the apparatus, where the substrate was exposed under vacuum with a pattern at a central portion of a toroidal pattern shown in
Thereafter, the membrane film 43 was dry-etched by oxygen gas plasma using the resist pattern 44a as a mask until the silicon oxide film 42 was exposed, so that a membrane film pattern 43a was formed (see
Next, resist was applied on a back face of the silicon substrate 40 and a resist pattern 45 was formed according to lithographic technique (see
Next, Example of the method for manufacturing a magnetic disk medium using the membrane mask (reticle) manufactured according to the manufacturing method of the Example will be explained with reference to
As shown in
A pattern reduced to an outer diameter of 0.85 inch corresponding to ¼ of a mask size was transferred on the resist by exposure via the above-described membrane mask using a reducing projection electron beam exposing apparatus. After exposure, a resist original disk with a resist pattern 24a was obtained by dipping the silicon substrate in developing solution for 90 seconds to develop the same, thereafter dipping the developed substrate in rinsing liquid for 90 seconds to rinse the same, and drying the substrate using air blowing (see
Next, as shown in
Thereafter, the resist original disk attached with the electrically conductive film 26 was electroformed for 90 minutes so that an electroformed film 28 was formed (see
Nickel sulfamate: 600 g/L
Boric acid: 40 g/L
Interfacial active agent (sodium lauryl sulfate): 0.15 g/L
Temperature of liquid: 55° C.
PH: 4.0
Current density: 20 A/dm2
A thickness of the electroformed film 28 obtained at that time was 300 μm.
Thereafter, a stamper 30 with the electrically conductive film 26, the electroformed film 28, and the resist residue was obtained from peeling off the electroformed film from the resist original disk (see
After the stamper 30 was cleaned for 15 minutes using asetone, the stamper was dipped in solution obtained by diluting fluoroalkyl silane [CF3(CF2)7CH2CH2Si(OMe)3](TSL8233 manufactured by GE TOSHIBA SILICON CORP.) to 5% solution using ethanol for 30 minutes and solution adhered on the stamper was blown off by a blower, the stamper 30 was annealed at 120° C. for 1 hour.
On the other hand, as shown in
A resist pattern 34a was formed by using an ICP (induction coupling plasma) etching apparatus to perform oxygen RIE on the resist film 34 on the substrate imprinted in the above manner under etching pressure of 2 mTorr (see
After the magnetic recording layer 32a was formed, a DLC (diamond like carbon) 36 with a thickness of 3 nm was formed as a protective film according to a CVD (chemical vapor deposition) process (see
Next, a method for manufacturing a reticle according to Example 2 of the present invention will be explained with reference to
As shown in
Next, the substrate thus obtained was conveyed to a predetermined position inside an electron beam lithographing apparatus (not shown) using a conveying system (not shown) of the apparatus, where a pattern shown in
Subsequently, anisotripic etching was applied to the SOI layer 52 using the resist pattern 53a as a mask until the silicon oxide film 51 was exposed, so that a patterned SOI layer 52a was obtained (see
Next, resist was applied on a back face of the silicon substrate 50 and a resist pattern 54 was formed according to lithographic technique (see
A magnetic disk medium was manufactured using the stencil mask according to steps similar to those in example 1. When the magnetic disk medium obtained in this manner was incorporated in a magnetic recording apparatus and signal evaluation was performed, an excellent magnetic signal could be obtained.
Each of the magnetic disk media explained in Examples 1 and 2 was a magnetic substance-patterned medium, namely, it is obtained by working a magnetic substance (a magnetic recording layer) formed on a substrate, but it may be a substrate-patterned medium. A method for manufacturing the substrate-patterned discrete track media (magnetic disk medium) will be explained as Example 3.
Next, a method for manufacturing a magnetic recording medium will be explained with reference to
First, an imprint stamper was manufactured according to an approach similar to the approach shown in
An undulated or corrugated substrate was manufactured using imprint lithographing process, as described below. As shown in
Next, a substrate 60a with the corrugated pattern was obtained by etching the substrate 60 using the resist pattern 61a as a mask. Thereafter, the resist pattern 61a was removed (see
Subsequently, as shown in
A magnetic substance portion and a non-magnetic substance portion of the magnetic film-patterned discrete track media described in
As described above, according to each of the embodiments of the present invention, a reticle which has a high strength even it is formed in a doughnut shape, a method for manufacturing a magnetic disk medium using the reticle, and a magnetic disk medium using the same can be obtained.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concepts as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-92759 | Mar 2005 | JP | national |
