Patent Application
20090166553
1. Field
One embodiment of the present invention relates to an electron beam drawing method for drawing patterns in a discrete track recording-type magnetic disk medium.
2. Description of the Related Art
In technical trends of high-density magnetic disks (hereinafter, also referred to as hard disks), so-called discrete track recording-type magnetic disks, in which magnetic patterns generating magnetic signals are separated by a nonmagnetic material, are proposed. The discrete-type magnetic disks have specific magnetic patterns in data zones on which user data are recorded and servo zones. In order to manufacture the discrete-type magnetic disks, it is advantageous that a stamper master having desired patterns is manufactured by lithography, and imprinting is carried out by using the stamper master.
Jpn. Pat. Appln. KOKAI Publication No. 2005-275186 discloses a method for drawing exposure patterns including track patterns of an information recording medium. In the drawing of circular patterns using a drawing apparatus having an X-Y movement mechanism, movement control of a stage is difficult, and an operation for controlling the drawing according to geometric patterns becomes complicated.
Jpn. Pat. Appln. KOKAI Publication No. 2002-288890 describes a beam irradiation method for irradiating an irradiation object with a beam while the beam is shifted to a movement direction of the object. This method, however, cannot cope with media such as discrete-type magnetic disks which have patterns not only in a circumferential direction but also in a radial direction and media which have patterns with a length of more than a possible deflection amount. When patterns in a form of bi-phase codes (also referred to as Manchester codes) which are used for address marks of a hard disk are drawn, a beam irradiation method for deflecting the beam not only to the movement direction of the object but also to the opposite direction depending on patterns is more preferable than the beam irradiation method for deflecting the beam simply to the movement direction of the object described in Jpn. Pat. Appln. KOKAI Publication No. 2002-288890. This is because, in this method, the deflection amount can be made to be a constant amount or less, namely, one-bit length or less through drawing.
In general, the magnetic disk drives have a donut-shaped magnetic disk, a head slider including a magnetic head, a head suspension assembly which supports the head slider, a voice coil motor (VCM) and a circuit board in a chassis.
The surface of the magnetic disk is defined by concentric tracks, and each track is divided into sectors every constant angle. The magnetic disk is mounted to a spindle motor to be rotated, and various digital data are written to and read out of the magnetic disk with a magnetic head. For this reason, the tracks are arranged in the circumferential direction, while servo marks for position control are arranged in the direction crossing the tracks. A servo zone includes sections such as a preamble section, an address section and a burst section. The servo zone may include a gap in addition to these sections.
In a stamper master used for manufacturing a discrete-type magnetic disk by imprinting, it is desired that both data zone and servo zone can be formed at the same time. This is because, when these zones are formed individually, alignment of these zones becomes difficult and complicated processes are required.
In order to manufacture the master, a photosensitive resin is exposed and developed by lithography so that patterns are formed. Since concentric circles should be drawn, drawing using an electron beam which can be deflected is preferable. Fine patterns like hard disk patterns whose track pith is of sub-micron should be connected accurately. For this reason, a system in which the stage continuously moves is more desirable than a so-called step-and-repeat system because the position control can be made stably.
When an electron beam is not deflected or is deflected slightly in order to draw a concentric circuit in the electron beam drawing apparatus, the electron beam is applied to a photosensitive resin film on the substrate through an aperture. On the other hand, when an electron beam is deflected strongly and is blanked so as to deviate from the aperture, non-exposed portions can be obtained. As a result, the exposed portion and the non-exposed portion are switched at a high speed, and thus patterns with clear edges can be formed.
As a way of stage rotation, CLV (constant linear velocity) or CAV (constant angle velocity) is generally used. CLV is desirable in that an exposure amount of an electron beam per unit area (or unit length) can be constant. In CLV, control is made so that an irradiation radius position r and a rotation number X of the stage per unit time establish an inversely proportional relationship, and a linear velocity Lv is kept constant.
On the other hand, high density is obviously required in discrete-type magnetic disks, and fine patterns are required to be drawn by electron-beam exposure in manufacturing a master. From view points of mass productivity and cost reduction, the electron-beam exposure in manufacturing the master is required to be carried out in as a short time as possible.
In the electron beam drawing, it becomes a problem that resolution is limited by space-charge effect of electron beam, in other words, that electrons traveling an optical path cause Coulomb interaction (space-charge interaction) through Coulomb reactive force exerting between them which in turn cause beam focusing blur, also referred to as Coulomb blur. It is known that the Coulomb blur a is proportional to a beam current I and an optical path length L and is inversely proportional to the three-halves power of an acceleration voltage V, as represented by the following formula (1).
σ∝IL/V3/2 (1)
According to the formula (1), decrease in the beam current I is effective for the drawing of fine patterns. In general, the optical path length L and the acceleration voltage V are often set to fixed values in the drawing apparatus. When the beam current I is low, however, the linear velocity is made to be slow so that a predetermined exposure amount should be obtained as long as sensitivity of a photosensitive resin is constant. For this reason, the drawing time becomes long, and thus the mass productivity is lowered.
In the discrete-type magnetic disk, patterns of a preamble section, address section and burst section formed in servo zones are defined by presence and absence of a magnetic material so as to constitute bi-phase codes (also referred to as Manchester codes) or the like. Thus, in general, when servo marks are formed by means of an r-θ type electron drawing apparatus, it is not necessary that portions to be exposed on a positive photosensitive resin film are continued by three bits or more, and also it is not necessary that an electron beam is applied to the photosensitive resin film on the substrate for duration of 50% or more.
As to the tracks arranged in the circumferential direction, it is sufficient only if a magnetic noise from an adjacent track is prevented, and thus a groove width between the tracks may be a half or less and more preferably ⅓ or less of the track pitch or less. When the track pattern is formed, therefore, it is not necessary that an electron beam is applied to the photosensitive resin film on the substrate for duration of 50% or more. Conventionally, when the patterns of the discrete-type magnetic disk are formed on the positive photosensitive resin film using the r-θ electron beam drawing apparatus, the time for which an electron beam is not applied to the photosensitive resin film by exerting blanking is a half or more of the entire drawing time, which leads to low productivity.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, there is provided an electron beam drawing method comprising: providing an electron beam drawing apparatus having a stage on which a substrate is placed, a movement mechanism which moves the stage to a horizontal direction and a rotation mechanism which rotates the stage; and placing the substrate, on which a photosensitive resin film is coated, on the stage, applying an electron beam to the photosensitive resin film while the substrate on the stage is rotated and moved to the horizontal direction, and drawing a pattern extending to a radial direction, characterized in that the electron beam is deflected to a direction parallel with a rotational direction of the substrate such that a relative movement speed of an electron-beam applied position on the substrate in the direction parallel with the rotational direction of the substrate becomes slower than a linear velocity of the substrate, viewed from a drawing start position in a circulation for drawing the pattern.
In the present invention, an electron beam may be deflected to a direction parallel with a rotational direction of a substrate and to a radial direction. In this case, a deflection amount in the radial direction is a pitch in the radial direction per rotation or less, and more preferably a half of the pitch or less. As a result, a pattern in the radial direction can be drawn smoothly.
Exposure with an electron beam may be started from an inner peripheral side or an outer peripheral side, or some divided zones may be exposed. In order to obtain an OFF state during the exposure of a portion corresponding to a bit pattern, a deflection signal may be given so that an electron beam is blanked in an electron beam drawing apparatus.
In the present invention, when assuming that a movement speed of the electron beam is V and a linear velocity of the substrate is L, an electron beam may be deflected so that the following relationship is satisfied: L/2≦V<L, and the electron beam applied position on the substrate moves to the same direction as the rotational direction of the substrate. An embodiment which satisfies such a relationship can be effectively used for a pattern which extends to the radial direction using description as bi-phase codes (also called as Manchester codes), in which the codes are arranged in a circumferential direction, or a pattern which extends to the radial direction and whose duty is 50% or less.
In the present invention, the electron beam is deflected to an opposite direction to the rotational direction of the substrate within a range which is twice or less of a bit length on a radial position where the bit is present at the time when that bit is started to be drawn. This embodiment can cope with a case where two bit portions to be exposed continue.
In the present invention, photosensitive resin may be positive resist or negative resist, and further chemically-amplified resist including a material which generates acid due to exposure (hereinafter, referred to as an acid-generating agent) or non-chemically-amplified resist. With the positive photosensitive resin, the areas to be exposed can be smaller than the negative photosensitive resin, and thus it is preferable in view of sensitivity and resolution. In particular, the non-chemically-amplified positive resist is preferably used because it has satisfactory sensitivity to an electron beam and is stable, and has satisfactory resolution. Materials mainly containing PMMA (polymethylmethacrylate) and novolac resin can also be used. Dry etching resistance is not particularly limited.
In the present invention, in drawing a pattern extending to a circumferential direction, an electron beam may be deflected to the radial direction in a circulation on a vicinity of the pattern, so that the pattern may be multiply exposed. According to this embodiment, also as to the pattern which extends to the circumferential direction, the drawing time can be shortened, and thus this embodiment is effective particularly for forming grooves between discrete tracks.
Examples of patterns to be formed by the method of the present invention include patterns of a discrete-type magnetic disk including a preamble pattern and a discrete track pattern.
An electron beam drawing method according to the embodiment of the present invention is described with reference to
The drawing method is described from macroscopic viewpoint.
On the contrary, the concept of the drawing method according to the present invention is shown in
In the pattern with a gap in the circumferential direction, when the electron beam irradiation position is moved to the circumferential direction, the electron beam irradiation time can be extended. In a case of a track pattern without a gap in the circumferential direction, however, when the electron beam irradiation position is moved to the circumferential direction, the electron beam irradiation time cannot be extended. In a circulation on the adjacent portion which conventionally does not generate a signal 1, the number of circulations with which the signal 1 is generated is increased so that the electron beam irradiation time extends to be b-times the conventional one at the circulation at which the signal 1 is generated. The “b” is preferably a numerical value close to the “a” in view of the adjustment of the exposure amount. If only such a numerical value is satisfied, a desired pattern cannot be obtained, blurred or thickened in the radial direction, and thus the beam irradiation position is collected to a position where the electron beam should be deflected and originally drawn, namely, a position which is irradiated in the conventional method. As to the pattern which extends to the radial direction, the electron beam is deflected as shown by arrows in
Also in conventional methods, the time 1 and the time 0 do not have to be equal to each other. When a positive resist is used, a pattern after development generally becomes larger than an exposure pattern. When a discrete-type magnetic disk medium is manufactured using imprinting, a pattern occasionally becomes thicker than a master during processes. For this reason, even when the pattern of 1:1 is desired on a medium, the exposure pattern does not always have to be formed at 1:1. For example, when a positive resist is exposed so that a master is manufactured, an exposed portion is formed in a recess and an unexposed portion is formed in a protrusion. When a stamper whose recess and protrusion are reversed is manufactured by using this resist pattern and the pattern is transferred using this stamper, a portion corresponding to the unexposed portion becomes a protrusion on the medium. When the recess becomes wide in processing the recess using the protrusion as a mask, unexposed portions corresponding to the widened recess of the medium should be provided at ratio larger than a desired ratio, and thus the ratio of the exposed portions is desirably a half or less.
Since the stage continues to rotate during drawing, when an electron beam is deflected to the circumferential direction and a pattern which extends to the radial direction is drawn, the electron beam is deflected to a direction parallel with a rotational direction of the substrate such that a relative movement speed of an electron-beam applied position on the substrate in the direction parallel with the rotational direction of the substrate becomes slower than a linear velocity of the substrate, viewed from a drawing start position in a circulation for drawing the pattern. In the case where the movement speed of the electron beam is V and the linear velocity of the substrate is L, if the relationship of L/2≦V<L is established, the blanking time is decreased, and the pattern can be drawn efficiently. For this reason, this method is preferable.
When two bits to be exposed continue, the following is performed. Before the substrate comes to a bit position of the two bits to be first exposed and when a bit start position one previous to the bit position to be first exposed is on a non-deflection drawing position, the bit to be first exposed is started to be drawn. An electron beam is deflected to the opposite direction to the rotational direction of the stage within a range which is not more than twice a bit length on the radial position where this bit is present at this time. The electron beam is deflected to the opposite direction to the rotational direction of the stage during the exposure of the first bit, and the electron beam is deflected to the same direction as the rotational direction of the stage during the exposure of the second bit. As a result, even when two bits to be exposed continue, the method of the present invention can be used effectively.
Also when the pattern which extends to the circumferential direction is drawn, the exposure time should be shortened. Thus, the electron beam is deflected to the radial direction in the circulation on a position vicinity to the pattern, and the pattern portion may be multiply exposed.
The discrete-type magnetic disk patterns such as the preamble pattern and the discrete track pattern can be formed in such a manner.
The stamper which is manufactured by using the electron beam drawing method of the present invention is described. The stamper may have a disk shape, a doughnut shape or another shape. A thickness of the stamper is desirably 0.1 mm or more and 2 mm or less. When the stamper is too thin, satisfactory strength cannot be obtained. When the stamper is too thick, electroforming requires long time, and thickness difference becomes large. A size of the stamper is preferably larger than the medium, but the size is not particularly limited. The resultant stamper is used for manufacturing the discrete-type magnetic disk by imprinting. The discrete-type magnetic disk may be magnetic film-patterned discrete track media or substrate-patterned discrete track media.
A method of manufacturing a stamper is described with reference to
As shown in
A method of manufacturing a magnetic film-patterned discrete-type magnetic disk using the stamper is describe with reference to
The shape of the substrate 11 is not particularly limited, but a disk shape is preferable, and a silicon wafer or the like is used. As the substrate, a glass substrate, an Al alloy substrate, a ceramic substrate, a carbon substrate, a compound semiconductor substrate or the like can be used. As the glass substrate, amorphous glass or crystallized glass can be used. Examples of the amorphous glass are soda-lime glass and aluminosilicate glass. An example of the crystallized glass is lithium-series crystallized glass. Examples of the ceramic substrate are sintered bodies mainly containing aluminum oxide, aluminum nitride or silicon nitride, and materials obtained by fiber-reinforcing the sintered bodies. Examples of the compound semiconductor substrate are GaAs, AlGaAs.
The magnetic disk preferably has a donut shape. A size of the magnetic disk is not particularly limited, but 3.5 inches or less is desirable so that the drawing time using an electron beam is not excessive. Further, 2.5 inches or less is desirable so that pressure in imprinting is not excessive. In view of the mass productivity, sizes of 1.8 inch, 1 inch or 0.85 inch are desirable so that the electron beam drawing time can be relatively short and the pressure in the imprinting can be low. A surface to be used as the magnetic disk may be single sided or double sided.
The surface of the magnetic disk is defined by concentric tracks, and sectors obtained by dividing each track at every constant angle are formed. Whereas the tracks are arranged in the circumferential direction, servo zones for position control are arranged in the direction crossing tracks. The servo zone includes sections such as a preamble section, an address section in which information about tracks or sector numbers are written, and a burst section for detecting relative position of a head with respect to a track. The servo zone may include a gap in addition to these sections. The magnetic disk is mounted to a spindle motor and is rotated, and various digital data are written and read out with the head.
The track pitch is required to be narrow in view of the improvement in recording density. On one track, a track magnetic pattern and a nonmagnetic material to be a separating portion are formed, and an address bit and a burst mark of corresponding servo zone should be formed. For this reason, a pattern is required to be drawn so that one track is formed by a several times or a several tens times of circulations in cutting. When the number of cutting circulations is small, shape resolution becomes low, and thus the pattern shape cannot be satisfactorily reflected. When the number of the cutting circulations is large, control signals are made complicated and their capacity increase. For this reason, it is desirable that one track is formed by circulations in a range of 6 or more and 36 or less. It is advantageous that the numerical value of the number of circulations has a lot of divisors in view of design for pattern arrangement.
Since the sensitivity of the resist to be exposed is normally uniform in the plane, it is desirable that the stage of the electron beam drawing apparatus rotates with constant linear velocity. For example, when the track pitch is 300 nm and one track is tried to be formed by 12 cutting circulations, the cutting track pitch becomes 25 nm (=300÷12). The cutting track pitch is desirably not more than a beam diameter in order to eliminate an insufficiently exposed area and an undeveloped area.
Examples of the present invention are described below.
An example that a discrete track medium is manufactured by using the methods shown in
An electron beam drawing apparatus whose acceleration voltage is 50 kV was used. The apparatus has a ZrO/W thermal field emission electron gun emitter including an electron gun, a condenser lens, an objective lens, a blanking electrode and a deflector.
On the other hand, resist ZEP-520 manufactured by ZEON corporation was diluted with anisole to two times, and was filtered by a membrane filter with 0.2 μm. After the stamper substrate 1 made of 8-inch silicon wafer subjected to HMDS treatment was spin-coated with a resist solution, the stamper substrate 1 was prebaked at 200° C. for 3 minutes, so that the resist 2 with thickness of 0.1 μm was formed (
The stamper substrate 1 was carried to a predetermined position in the electron beam drawing apparatus, and was exposed under vacuum and the following conditions so that concentric patterns were drawn (
Radius of the exposed portion: 4.8 mm to 10.2 mm
The number of sectors/track: 150
The number of bits/sector: 4000
Track pith: 300 nm
A moving amount per one rotation: 20 nm
The number of exposure circulations per track: 15 circulations
The number of exposure circulations per burst mark: 10 circulations
Linear velocity: 1.0 m/s (constant)
At this time, deflection strength was gradually increased during one rotation, and a concentric circle was drawn. The servo zone includes a preamble pattern, a burst pattern, an address pattern, and a gap. The tracks occupy 90% of the area of sectors.
When the preamble pattern, the burst pattern and the address pattern on the servo zone were exposed, an electron beam was deflected to the circumferential direction, and the movement speed of the beam was 0.6 m/s. On an angle position where a groove of the track was present, one track was exposed in 8 circulations and was not exposed in 7-circulations. The electron beam was deflected to the radial direction in each two circulations of the 8 circulations from the outer side, so that these electron beams were uniformly overlapped with electron beams on the inner four circulations.
The stamper substrate 1 was immersed into a developer (for example, ZED-N50 manufactured by ZEON corporation) for 90 seconds and the resist was developed. Thereafter, the stamper substrate 1 was immersed into a rinse liquid (for example ZMD-B manufactured by ZEON corporation) for 90 seconds so as to be rinsed. The stamper substrate 1 was dried by air blow, so that the resist master was manufactured (
The conductive film 3 was formed on the resist master by sputtering. Pure nickel was used as a target, and the sputtering camber was evacuated to 8×10−3 Pa. Thereafter, argon gas was introduced into the sputtering camber and adjusted to 1 Pa, and a DC power of 400 W was applied, and sputtering was performed for 40 seconds, so that the conductive film 3 of 30 nm was obtained (
The resist master with the conductive film 3 was electroformed for 90 minutes by using nickel sulfamate liquid (NS-160 manufactured by SHOWA CHEMICAL CO., LTD) (
Nickel sulfamate: 600 g/L
Boric acid: 40 g/L
Surfactant (sodium lauryl sulfate): 0.15 g/L
Liquid temperature: 55° C.
pH: 4.0
Current density: 20 A/dm2
A thickness of an electroformed Ni film 4 was 300 μm. The Ni film 4 with the conductive film 3 was peeled from the resist master so that the stamper 5 was obtained (
After the stamper 5 was sonic-cleaned for 15 minutes by acetone, the stamper 5 was soaked in a solution which was obtained by diluting fluoroalkylsilane [CF3(CF2)7CH2CH2Si(OMe)3] (TSL 8233 manufactured by GE Toshiba Silicones Co., Ltd) to 5% using ethanol for 30 minutes. After the solution was blown away with a blower, the stamper 5 was annealed at 120° C. for 1 hour.
The magnetic recording layer 12 was deposited on the donut-shaped glass substrate 11 of 0.85 inch by sputtering, and was spin-coated with novolac resist (S1801 manufactured by Rohm and Haas Company) 13 at 3800 rpm (
The imprinted substrate 11 was subject to oxygen RIE under the pressure of 2 mTorr by using an ICP (induction coupled plasma) etching apparatus. Resist residues remaining on the bottoms of the recesses of the resist 13 were removed so that the resist patterns 13a were formed (
The discrete track medium which was manufactured in such a manner was incorporated into a magnetic recording apparatus, and signals were detected. As a result, satisfactory burst signals were obtained, and head positioning could be controlled suitably. The grooves between the tracks had a width of 85 nm.
An example that a substrate-patterned discrete track medium is manufactured by using the method shown in
A stamper was manufactured by the method shown in
A substrate having patterns of protrusions and recesses is manufactured by using imprint lithography.
As shown in
The obtained discrete track medium was incorporated into a magnetic recording device and signals were detected. Satisfactory burst signals were obtained, and head positioning could be controlled suitably. The grooves between the tracks had a width of 85 nm.
An example where a discrete track medium is manufactured by using the methods shown in
The electron beam drawing apparatus similar to example 1 was used. The resist 2 was applied to the substrate 1 similarly to example 1 (
The discrete track medium which was manufactured in such a manner was incorporated into the magnetic recording apparatus, and signals were detected. As a result, satisfactory burst signals were obtained, and head positioning could be controlled suitably.
The substrate was rotated at a speed which is half of that in the example 1 in drawing, and an electron beam was not deflected except for the deflection in drawing concentric circles. A beam irradiation time was reduced to half on the servo zone having a pattern in the radial direction, and an electron beam drawing on the grooves between the tracks was carried out in four circulations per track. Except for these conditions, conditions similar to those in example 1 were used, so that a discrete track medium was manufactured.
With this method, the discrete track medium similar to that in example 1 could be obtained, but it took a double time to manufacture the stamper.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-173475 | Jun 2007 | JP | national |
This is a Continuation Application of PCT Application No. PCT/JP2008/061807, filed Jun. 24, 2008, which was published under PCT Article 21(2) in English. This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-173475, filed Jun. 29, 2007, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2008/061807 | Jun 2008 | US |
| Child | 12400254 | US |
