WO2009041816A2 - A method of patterning a hard disk medium - Google Patents

Abstract

The invention relates to a method of patterning a hard disk medium, comprising the step of applying a lithographic process to a resistive top layer of the hard disk medium, wherein the resistive top layer is exposed to a beam having multiple electron or optical beamlets. Preferably, foci of the multiple beamlets are arranged at different radial distances from a center point of the hard disk, more preferably substantially on a line extending from the center point of the hard disk to an edge of the hard disk.

Description

Title: A method of patterning a hard disk medium

The invention relates to a method of patterning a hard disk medium, comprising the step of applying a lithographic process to a resistive top layer of the hard disk medium.

Conventionally, Hard Disk Drives (HDD) comprise recording media having a thin granular film of a hep Co-based alloy, typically including some combination of Pt, Cr, B and Ta, sputter deposited onto either a glass or NiP- coated aluminum substrate. The film stack typically includes various underlayers or seed layers below the magnetic film, and protective overcoats such as carbon on top of it. The grains in the magnetic film are randomly oriented and positioned in the plane of the film.

In the field of HDD's there is a need to increase the density of information. For many years this has been realized by decreasing the size of the magnetic grains in the magnetic media of HDD's. However, the grains cannot shrink further since they will get thermally instable. As a result the data will erase itself.

A realistic scenario to increase the information density without decrease of the grain size, is to work with even larger grains that are physically separated, thus forming patterned media.

Figure Ia shows a schematic perspective view of an artificial hard disk 1 having a first semi disc 2 configured as a conventional multigrain medium and a second semi disc 3 configured as a patterned magnetic medium. Both media types are shown in more detail in partially enlarged sections 4, 5, 6. In the most enlarged section 6 individual bit cells having a bit cell distance 7 are shown. The bit cells are positioned in a track 8 being a trace on a specified distance with respect to a center point of the disk 1. In the conventional multigrain medium, individual grains 9 are visible. The dark sections correspond with regions where the magnetization polarization is in a first direction while white sections correspond with regions where the magnetization polarization is in a second, oppositely oriented direction. Transitions between magnetization polarization are coupled to corresponding data bits 12. A typical radial distance 13 between subsequent tracks 8 is approximately 100 micro meter. Similarly, the most enlarged section in Figure Ia shows individual bit cells formed as patterned islands 11 having one of two magnetization polarization directions. A typical radial distance 13 between subsequent tracks 8 is approximately 40 micro meter.

Figure Ib shows a HDD writer/reader 14 comprising an actuator 15 having a disk head 17 that is provided with elements for writing and/or reading data present on a track 18 of a disk 1. The head 17 is positioned above the disk 1, supported by an air bearing surface flying above the hard disk surface at small heights, such as up to 10 nm spacing and at linear velocities up to greater than 40 m/s. Proper positioning of the actuator 15 is performed by a pusher 16 being under interferometer control.

Figures 2 and 3 show in more detail a schematic perspective view of a writing/reading head 20 operating above a continuous medium track 8 and a patterned medium track 8, respectively. The head 20 is provided with an inductive write element 21 and a GMR read element 22. Magnetization polarization directions of the individual grains 9 and patterned islands 11 are symbolically denoted by arrows 19.

Future developments of patterning of the media is likely to happen in two subsequent steps, viz. as a first step realizing discrete track recording (DTR) media for hard disks wherein grooves are created to separate the pixels in at least one direction, see e.g. Figure 4a, and as a second step realizing bit patterned media (BPM) for hard disks wherein pixels are separated in a further direction to further increase the information density on the media, see e.g. Figure 4b. The discrete track recording medium 23 shown in Figure 4a comprises tracks 25 of magnetization material arranged in parallel and separated by channels 26. The bit patterned medium 24 shown in Figure 4b comprises isolated islands of magnetization material 11 separated by channels 27 crossing each other in a two-dimensional plane.

Figure 5a shows a process flow 100 for manufacturing continuous media. In a first step 101 a substrate is machined and grinded. In a second step 102, the substrate is annealed and NI plated. The third step 103 includes polishing and cleaning of the substrate. Then, in a fourth step 104, magnetic media is deposited and lubricated. Subsequently, in a fifth step 105 of the process, the surface of the thus obtained magnetic medium is tested and certificated. The first to fifth steps 101-105 are usually performed at the media supplier. As a sixth step 106, servo tracks are written and tested. Further, as a seventh step 107, the HDD is assembled. Typically, the sixth and seventh step 106, 107 are carried out at the site of a HDD manufacturer.

Figure 5b shows a process flow 120 for manufacturing bit-patterned media (BPM) media. Several steps remain similar, such as the first to third steps 101-103, the surface testing and certification step 105 and the assembly step 107. However, before performing the fourth step 104, viz. depositing magnetic media and lubrication of the media, the process flow 120 for manufacturing bit patterned media comprises the step of patterning bits including a servo track 108. Further, the sixth step 106 of writing and testing service tracks has been removed.

According to Figure 5b, the bit patterning step 108 comprises a number of sub-steps, viz. producing a stamp or mask 110, a polymer coating step 111, a step of actually performing an imprinting process or lithography process, using the earlier produced stamp or mask, respectively, a developing step 113, a cleaning step 114 and an inspection step 115. Consequently, the process of patterning itself, viz. the imprint process or the lithography process, is surrounded by several pre-processing and post-processing steps like spinning and development of resist. For the pattering itself most likely a mask or stamp is needed. Finally, it is assumed that the pattern is inspected for defects similar to the situation in IC production. At first sight, patterns on HDD-media seem comparable to those on DVD/CD. However, there are also important differences. On a hard disk 1 the data are stored in sectors 28 and tracks 29, see e.g. Figure 6a showing a schematic top view of a hard disc. Further, the sectors 28 are logically combined in clusters. Databits of information can be stored independently of each other, in principle on any possible location on the hard disk 1 because of a defragmentation requirement. On a DVD/CD 30, data are stored more or less sequentially on a single continuously spiralling track 31, see Figure 6b, showing a schematic top view of a DVD/CD. In this context it is noted that in case of both hard disk and CD/DVD, optionally with blue ray technology, data are scrambled and an error correction protocol is incorporated. As a consequence, sequential data are not written sequentially, even not in the case of CD/DVD.

A further difference between both types of media is the resolution capability. Currently, the resolution of Blue ray DVD technology is approximately 150 nm, while a substantially lower resolution is required in case of patterned HDD media.

In continuous HDD-media each hard disk has head tracking servo information written on about 10% of the disk surface. These servo patterns occur periodically along every track, typically 100 times per revolution. The servo patterns are created on a track-by-track "servowriting" operation, while an external pushing element 16 guides the head 17 during servo writing. The whole process takes about 30 minutes per drive. In contrast therewith, in patterned HDD-media accurate servo features are created along with data track islands, so that a need for performing a separate servowriting operation before actually operating the disk is eliminated.

In general, HDD media have to satisfy a number of specific geometrical requirements, such as a maximal ellipticity of the disc, a size tolerance of an individual patterned bit, a tangential pitch local variation and a global variation of an individual patterned bit over the disk, a shape tolerance of the individual patterned bit, a radial pitch tolerance, jitter requirements, a local placement to angular position with respect to a next track, a size tolerance of a servo pattern and a density variation of servo patterns within a sector and over the disk. Further height variation specifications, residual layer variation specifications and substrate flatness requirements have to be met.

In order to save costs, a master mask or stamp is realized, which master mask or stamp is replicated into daughter masks or stamps using optical lithography methods. The daughter masks or stamps directly serve for producing patterned hard disk media. In this approach expensive master masks or stamps are used efficiently.

In order to manufacture hard disk drives having bit patterned media, an electron beam or optical beam generating lithography system 40 is employed as shown in more detail in Figure 7. The system 40 comprises a source 41 emitting an electron beamlet or a photon beamlet 42, preferably with high brightness. The beam 42 is focused by means of a lens system 46a,b,c on a small spot 43 at a top layer of a substrate 44 that is arranged in a vacuum chamber 45. The top layer comprises material that is resistive with respect to the electron beamlet or optical beamlet. The system further comprises one or more blanking elements 47 for deflecting the beam 42 in a direction such that the electrons or photons cannot reach the substrate 44. In this way the beam 42 can be switched on/off. The substrate 44 is mounted on a rotating stage 48 in the vacuum chamber 45. During operation of the system 40, the stage 48 rotates the substrate 44 and a pattern is written in the resistive layer on top of the substrate 44.

In using electron beam or optical beam technology, a field stitching problem arises. Known rotating stages may reach a required positioning accuracy, however, positioning the focus of the beamlets up to a required accuracy is far from trivial. Further, a time needed for writing an entire pattern in a hard disk might be relatively long, e.g. approximately 20 hours or longer, typically 100 hours, even after optimizing diffraction, source brightness and/or aberrations, during which time the system stability can not always be guaranteed, thus causing further inaccuracies. Consequently, a writing time is limited by either the blanking speed or the beam current in combination with a resist sensitivity of the substrate. Moreover, shot noise might be a further risk. Only a limited number of electrons or photons will reach a pixel area, resulting in a roughness at the edges of the patterned features.

It is an object of the invention to provide a system having an increased patterning speed. Thereto, according to the invention, the resistive top layer is exposed to a beam having multiple electron or optical beamlets. By using a beam having multiple electron or optical beamlets, the resistive top layer of the hard disk can be patterned at different locations simultaneously, thus advantageously enhancing the patterning speed of the system. Alternatively, the system for generating an electron beam or optical beam is replaced by a system for generating an ion beam or an X-ray beam. Further, atomic force microscopy technology or a self assembly technology can be used for forming the pattern in the substrate. Obviously, also a combination of the above-mentioned technologies can be applied. Other advantageous embodiments according to the invention are described in the following claims.

By way of example only, embodiments of the present invention will now be described with reference to the accompanying figures in which

Fig. Ia shows a schematic perspective view of an artificial hard disk having a first semi disc configured as a conventional multigrain medium and a second semi disc configured as a patterned magnetic medium; Fig. Ib shows a hard disc drive writer/reader;

Fig. 2 shows a schematic perspective view of a writing/reading head in more detail operating above a continuous medium track; Fig. 3 shows a schematic perspective view of a writing/reading head in more detail operating above a patterned medium track;

Fig. 4a shows a schematic perspective view of a discrete track recording medium; Fig. 4b shows a schematic perspective view of a bit patterned medium;

Fig. 5a shows a process flow 100 for manufacturing continuous media;

Fig. 5b shows a process flow 100 for manufacturing bit patterned media;

Fig. 6a shows a schematic top view of a hard disc;

Fig. 6b shows a schematic top view of a DVD/CD;

Fig. 7 shows a schematic cross sectional side view of a system for generating an optical or electron beam; Fig. 8 shows a simplified schematic cross section side view of a system according to the invention;

Fig. 9 shows a simplified schematic cross section top view of the system of Figure 8;

Fig. 10 shows a simplified schematic cross section top view of a further system according to the invention;

Fig. lla-c show fabrication steps of a number of NIL technologies;

Fig. 12a-c show first and second imprint results using NIL technologies;

Fig. 13 shows a schematic partial side view of a stamp during an imprint process in detail;

Fig. 14 shows steps of a disk imprinting process according to the invention; and

Fig. 15a shows a stamp according to the invention in a first state; and Fig. 15b shows the stamp of Fig. 15a in a second state. It is noted that the figures shows merely preferred embodiments according to the invention. In the figures, the same reference numbers refer to equal or corresponding parts.

Figure 8 shows a simplified schematic cross section side view of a system 140 according to the invention for generating of multiple optical beamlets or multiple electron beamlets 42. The system 140 comprises elements that are similar to the system 40 shown in Figure 7. However, the system 140 according to the invention is arranged for generating multiple beamlets 42, not a single beamlet. The foci 49 of the beamlets 42 expose the top layer of the hard disk 44, so that a patterned top surface is obtained. The hard disk 44 is supported by a stage 48 rotating in a rotating direction R. The beamlets 42 are generated either from multiple sources or from a single source. Further, an individual beamlet 42 can be deflected by activating blanking elements. Thereby individual foci 49 can be switch on and off. Optionally, the system 140 comprises means for measuring a position of a radial outer beam 42 and for measuring the position of the hard disk 44, and means for activating or deactivating an radial outer beamlet via the blanking elements in response to signals that are output by a controlling mechanism in dependence of the above-mentioned measurements. In an embodiment according to the invention, foci 49 of the multiple beamlets are arranged at different radial distances from a center point of the hard disk 44. By simultaneously writing in regions near the center and more remote from the center, a positive impact on the overall throughput and on a lateral range of the rotating stage is obtained. Figure 9 shows a simplified schematic cross section top view at the level of the hard disk surface of the system 140 according to the invention. Foci 49a of multiple beamlets 42 are located on a virtual line 50 extending from the center point C of the hard disk 44 to an edge 52 of the hard disk 44. Consequently, each focus 49a on the line 50 has a unique radial distance with respect to the center point C. Further foci 49b are positioned on a second virtual line 51a extending from the center point C to the edge 52, so that foci 49a,b are arranged at different peripheral positions with respect to the center point C. Similarly, additional foci 49c, 49d are positioned on additional virtual lines 51b, 51c. As a result, the patterning speed can be further increased. It is noted that the foci can also be positioned on another number of lines, e.g. ten lines, or on a single line extending from the center point C to the edge 52, e.g. a single straight or curved line, or a single line extending along a finite radial distance over the disk 44. The additional virtual lines 51b, 51c extend from the edge 52 radially in the direction of the center point C. The loci of the additional foci mainly concentrate in a direction towards the edge 52 so as to cover not merely locations near the center point C but also locations near the edge as is explained below. Therefore, first ends of the virtual lines are located at the edge 52 of the hard disk 44, while other ends of the virtual lines can be located at a certain distance from the center point C without actually reaching the center point C.

Figure 9 further shows that the number of beam foci 49 increases as a function of its relative radial position with respect to the center C, so that more beamlets are available for patterning a section that is further radial removed from the center C. In this way, the individual beamlets 42 of the system 40 can operate efficiently when patterning the disk surface, as the area to be treated also increases as a function of its relative radial position. In particular, the density of beamlet foci 49 increases when the radial distance with respect to the center C increases. Consequently, a substantially similar area fraction size of the disk surface is exposed by each beamlet, thus enhancing the average and hence the overall productivity. Alternatively, beamlet foci 49 can be added at further peripheral positions with respect to the center C.

Figure 10 shows a simplified schematic cross section top view at the level of the hard disk surface of a further system according to the invention. Here, foci 49 of the multiple beamlets 42 are arranged densely in a two- dimensional segment 53 over the top layer of the hard disk 44. The segment 53 is pie-shaped, so that areas patterned by the beam 42 are substantially equal in size. The pie-shaped segment 53 is substantially uniformly occupied by multiple beam foci 49, optionally thousands of beam foci 49. A mutual distance 55 between adjacent beam foci 49 is e.g. approximately 125 micro meter.

Obviously, also other mutual distances between beam foci can be applied, e.g. more than approximately 125 micro, such as approximately 250 micro meter, or even less than approximately 125 micro meter, e.g. approximately 100 micro meter. Further, the segment 53 can be occupied non-uniformly by multiple beam foci 49. Instead of shaping the segment 53 as a pie, also other shapes can be chosen, e.g. a rectangular shape.

Optionally, the position of individual beamlet foci 49 can be deflected in a predefined distance range, thereby advantageously rendering a lateral stage motion superfluous. The deflection can be activated by deflecting elements, based on electric and/or magnetic field.

More generally, according to an aspect of the invention, a position of individual beamlet focus 49 is deflected as a function of time to pattern the underlying structure of the disk 44. The deflection can be performed in a radial and/or peripheral direction, thereby minimizing a non-operating blanking time of individual beams. In this way, the beamlets operate more efficiently.

According to another aspect of the invention, the stage 48 supporting the disc 44 performs a substantially uniform movement in a lateral direction while a beamlet 42 is deflected stepwise from a first radial deflected position to a second radial deflected position. As an example, the beamlet 42 is deflected from a radial inwardly deflected position to a radial outwardly deflected position. This aspect of the invention is partially based on the insight that particles in the beamlet have a relatively low mass or no mass at all, so that the stepwise deflection step can be performed without substantial time loss. In contrast to prior art systems wherein a beamlet position is fixed and wherein the stage performs stepwise lateral movements with high accuracy to expose a particular ring segment of the disk, the transition to patterning an adjacent ring segment can be performed relatively fast with relatively large accuracy. During patterning a specific ring segment of the disk, the beam can be continuously deflected for following the lateral movement of the supporting stage 48. Obviously, the stage 48 can simultaneously perform a rotation movement.

It is noted that in prior art systems stitching accuracy problems arise when starting and finalizing patterning a ring segment of a substrate. In according with one aspect of the invention, the ring segment is patterned during multiple passes of the respective segment, thereby smoothening the stitching effect at the starting and finalizing instant of the patterning operation. According to a further aspect of the invention, the begin section and the end section of the patterned ring segment overlap at least partially, thereby also smoothening the stitching effect. In order to minimize local overdose effects, the intensity of the beamlet during the start section and the end section is optionally reduced.

In order to further improve a position accuracy of a hard disk with respect to a beam, according to the invention, the stage 48 supporting the disk 44 is borne by an air bearing in vacuum, e.g. facilitated with a differential pumping. Further, a position of an e-beam relative to the stage position can be monitored continuously and can be corrected by deflecting the beamlet. According to another aspect of the invention, accuracy errors are minimized by adjusting the rotating speed of the stage 48 to an eigenfrequency of an beam intensity, e.g. 50 Hz. Especially, the rotation speed of the stage 48 is adjusted so that an integer number of eigenfrequency periods pass during a single revolution of the stage.

In prior art systems beam metrology is performed by measuring positions of optical components. In order to enhance the beam metrology it is proposed, according to an aspect of the invention, to segment the aperture through which a beamlet passes and measure electrical currents on each segment to thereby providing information concerning beam position and drift at the position of the aperture. Further, according to a further aspect of the invention, a detector, such as a Faraday cup 98, can be used to measure a beamlet position of a reference beamlet 99, see e.g. Figure 8. Also, neighbouring beamlets can be used to measure a position of a beamlet. Further, a mutual position between a detector and the disk can e.g. be measured by interferometry. According to a further aspect of the invention, a resist thickness can be measured to determine a position of a beam with respect to the disk. From thus obtained position information position errors can be corrected.

Further, some beamlets can be used for patterning while other beamlets can be used for inspection so that a patterning process and an inspection process can be carried out on the fly.

It is known that light optical beamlets have limited resolution which is mainly due to diffraction effects. According to aspects of the invention the resolution is reduced thereby allowing light optical methods to patterning a hard disk. Advantageously, optical methods are relatively mature. According to a first aspect, immersion fluid is applied between the lens and the substrate in far field thermal patterning. According to a further aspect, light is permitted to reach the substrate only at specific angles that are selected to achieve a higher resolution. This technique can be combined with water based immersion in combination with thermally activated resist. Further, a so-called mid field lithography can be applied wherein a diffraction effect is at least partially compensated by the effect of phonons in a region of several micrometers after an aperture plate. According to a further aspect, near field lithography can be applied wherein the lens and the substrate are brought in close proximity to each other to counteract diffraction effects. Further, shorter optical wavelengths can be applied, e.g. extreme ultra violet, having a wavelength of e.g. 13 nm or a H2O source can be used operating at 4 nm wavelength. Optionally, the beam can be focussed using Fresnel lenses. Additionally, interference lithography can be applied. In such a process, optical beamlets mutually interfere to create a desired high-resolution dot pattern being a main structure for patterned hard disks. Specifically, unique patterns like servo patterns can be added later using electron beam technology since these servo patterns have to be added in a limited area. Advantageously, thus a high resolution and a high throughput can be obtained.

Alternatively, ion beamlets can be used instead of electron beamlets. Ions are heavier so that they face less influence from electro-magnetic stray fields. Furthermore they have a self cleaning effect since they sputter the contamination. Traditionally only Ga- sources are available with high brightness. However, also a He-source being a gas-field-ion- source having a high brightness can be used. It is noted that ion beamlets are influenced more severely by Coulomb interaction effects than electron beamlets. Also X-rays form an alternative to electron beamlets.

Advantageously, X-rays have shorter wavelengths and generates a dot pattern that is in principle suitable for generating a main structure for patterned hard disks.

For cost efficient pattern replications in the micro- and nanometer range, nano imprint lithography (NIL) systems are available. Such systems are suitable for imprint on various substrates, e.g. Si, GaAs and InP substrates as well as on polymers, ceramics, and metal substrates. Typical application areas include micro and nano structuring in data storage-, optical-, medical-, and molecular electronic- and mechanical devices. In order to imprint a surface using NIL technology three basic components are required, viz. a stamp with a desired pattern structure, a substrate material to be printed, e.g. comprising a layer of polymer of a few 100's nm spun on basic material of a substrate, and a printing equipment wherein temperature and pressure are adequately controlled and wherein the stamp and the substrate can be aligned with respect to each other. NIL technology has important advantages over conventional nano fabrication methods. In applying NIL technology, a flexible, low-cost and biocompatible fabrication technique is used that allows efficient mass replication of extremely fine patterns. Figure lla-c show fabrication steps of a number of NIL technologies.

It is noted that a substantial difference between the shown NIL technologies relates to the way wherein a solidification process if performed.

Figure 11a shows a so-called hot embossing technology being a low cost, flexible fabrication method, which has demonstrated polymer high aspect ratio microstructures as well as nanoimprinting patterns. Here, polymer substrates 61 are imprinted using a master stamp 60 comprising e.g. Nickel or Silicon material and having a preformed pattern 62 shown in the upper most section of Figure 11a. In a lower section, a step is shown wherein the stamp 60 is pressed on the substrate 61 under relatively high temperature and pressure conditions. In a further lower section, the stamp 60 has been removed and a patterned structure 63 on the substrate 61 is obtained. In the lower section of Figure 11a a final substrate having a patterned structure 64 is shown resulting after standard lithography steps have been carried out. By using a stamp 60 many fully patterned substrates can be created, the substrates comprising a wide range of materials. Hot embossing is therefore suited for applications from rapid prototyping to high volume production. Hot Embossing can be applied in a wide variety of fields: μTAS, microfluidics (micromixers, microreactors), micro-optics (wave guides, switches) etc. The main application is, however, in the production of CD's and DVD's. It is a cheap technique with relatively low performance on alignment and stamp lifetime. The relatively short stamp lifetime of the stamp is directly related to the yield of the process as is explained in more detail below.

Figure lib shows a second NIL technology, called UV-Nanoimprint Lithography. The UV-Nanoimprint Lithography (UV-NIL) technology uses also a stamp 60 having a preformed pattern, e.g. in quartz material 66. Further, low viscose materials are used, which materials are cross-linked during a UV 65 exposure process forming hard polymer features. Generally, alignment features of UV-NIL and stamp lifetime are significantly better compared with the hot embossing technology. Figure lie shows a third NIL technology, called Micro Contact

Printing. Here, a stamp 60 provided with ink droplets 67 transfers the droplets 67 to a novel metal surface just by a soft contact, which forms a self-assembled monolayer (SAM). In this method soft stamps like PDMS are used. The process can be performed at room temperature and under low contact forces, e.g. below circa 100 N.

The master stamp 60 in the above-mentioned technologies can be obtained using the earlier described electron beam or optical beam generating lithography system.

In applying a NIL technology, a number of aspects may be relevant for the process, e.g. fidelity of nano-scale features, adhesion of pattern particles to the substrate, a release of the stamp from the substrate, control of a residual layer on the substrate, time of curing of the patterned substrate wherein a relatively short time of curing reduced the chance of oxygen inhibition, stamp replication and stamp lifetime, the etch resistance of resist for transferring the imprinted pattern to a final pattern on the substrate, up- scaling aspects, e.g. to large areas and/or to double sided imprinting, a readily displacement during an imprint process, photo-polymerization time during exposure, volumetric shrinkage aspects of the imprinted pattern leading to feature fidelity problems, etch selectivity of materials for transferring the imprinted pattern to a final pattern in the substrate, adhesion aspects of imprinted material combined with release aspect of this material with respect to the stamp, material composition, e.g. formulation of monomers and DMS derivatives and a current dose, e.g. in a range of 20 - 50 mJ/cm2 at 365 nm radiation. Under reference to Figure 12a-c showing first and second imprint results using NIL processes, release aspect of NIL processes are explained in more detail. On the left-hand side, a stamp 60 and substrate 62 are shown after a first imprint, while on the right-hand side, a stamp 60 and substrate 62 after a second imprint following the first imprint, are shown. In Figure 12a the first and second imprint are executed without imprint release problems. In Figure 12b, an imprint release problem occurs during the first imprint. Here, printed material 68 sticks in a corresponding hole in the pattern 62 of the stamp 60. The printed material 68 is not released during withdrawal of the stamp 60 from the imprinted substrate 62. However, during the second imprint, following the first imprint, again no imprint release problem occurs and the printed material 68 is released from the stamp 60. Figure 12c shows a situation wherein the first imprint has the same problem as in Figure 12b. During the second imprint, the printed material 68a still sticks in the corresponding hole in the pattern 62 of the stamp 60. Further, a second amount of printed material 68b sticks in a hole corresponding therewith in the pattern 62 of the stamp without releasing it on the substrate 61. Therefore the printed pattern 63 on the substrate 61 lacks two pattern segments.

Figure 13 shows a schematic partial side view of a stamp during an imprint process in detail. More specifically, Figure 13a shows in the lower view an extending portion 70 of the pattern 62 of the stamp 60 during pressing the stamp 60 in a substrate 61 and in the upper view during withdrawing the stamp 60 from the substrate 61. The extending portion 70 substantially has a cylindrical shape having a length h, a cross sectional area A and a diameter D. In the upper view of Figure 13a substantially the entire extending portion 70 forming the pattern on the stamp 60 is withdrawn in a direction F, released from the substrate 61, so that a hole 71 is formed in the substrate 61 forming a pattern 63. As a consequence, the stamp 60 can be used for generating a second pattern in a second substrate. Figure 13b shows corresponding views in an upper and lower view. However, the extending portion 70 of the stamp 60 is now not entirely released by the substrate, so that the hole 71 is partially filled with stamp material. The pattern 63 in the substrate 61, as well as in the pattern 62 of the stamp 60 has now a defect. It is noted that such release problems shorten the lifetime of the stamp 60 considerably. One of the problems encountered in applying a NIL technology is a relatively low throughput of imprinted substrates. As an example, one patterned hard disk is obtained per minute.

In order to improve the throughput, a multiple number of imprint tools are arranged, according to the invention, so that hard disks can be processed in parallel. Thereto, an imprint system for patterning hard disk media is provided, comprising imprint tool modules for forming a multiple number of imprint tools serving as parallel production lines for the hard disk media, wherein at least one imprint tool module having a relatively short cycle time is shared by a multiple number of imprint tools. As an example, several tens of imprint tools are installed, e.g. 35 imprint tools. To render the entire system efficient, one or more modules of an imprint tool are used in common. As an example, an imprint tool comprises a handling module for moving disks, a cleaning module, a spinner to deposit a layer of liquid on a disk, a contact module wherein a particular disk is brought into contact with a stamp, a DUV exposure module for hardening the liquid and a release module wherein the disk and the stamp are separated. A most time consuming module, e.g. the contact module, is used as a separate module in each imprint tool. However, an exposure station has a relatively short cycle time. Therefore, a reduced number of exposure stations is enough to handle the throughput. In this way a cost optimization can be performed without reducing the throughput of the imprint tools.

An aspect ratio of a pattern is defined as a height of an extending portion with respect to its width. In order to provide a high-yield imprint method generating high aspect ratio patterns, a method according to the invention realizes in a first step an imprint comprising a relatively thin layer of resist and in a second step the thin patterned layer functions as a hard mask for generating a relatively thick second layer using an etch-technology, e.g. reactive ion etching.

Further problems causing a low imprint yield are patterns collapsing during withdrawal of a stamp from a substrate and stamp wear being the problem that resist particles release from the substrate and stick to the stamp thereby contaminating the disk pattern.

Thereto, according to the invention, the stamp and disk are brought into contact with each other via an intermediate liquid under low atmospheric conditions thereby preventing air inclusions between the stamp and the disk. Figure 14 shows steps of a disk imprinting process according to the invention. Figure 14a shows a stamp 60 having a pattern 62 to be imprinted on a substrate. The stamp 60 is supported by a holder 81. Further, Figure 14b shows that a liquid 80 is delivered to the patterning stamp 60. Optionally, a spinning technique is employed to form a substantially uniform layer. Then, Figure 14c shows that the liquid 80 is hardened using a DUV exposure module 82. Thus, the entire disk is formed by the hardened liquid 80. Advantageously, no external disk is required. It is noted that the hardened liquid 80 should have sufficiently mechanical strength. In addition, Figure 14d shows a vacuum chuck 83 so that a more or less uniform force can be applied to carefully release the stamp 60 from the hardened disk 80. Figure 14e shows the thus obtained disk structure 80 having a pattern 63 corresponding to the pattern 62 of the stamp 60.

Figure 15a shows a stamp 90 according to an aspect of the invention, in a first state. The stamp 90 comprises a multilayer structure. The structure comprises a hard basic layer 91. Further, the structure comprises a hard top layer 93 comprising a pattern 92 to be imprinted on a substrate. Between the hard basic layer 91 and the hard top layer 93 an intermediate fluid layer 94 is sandwiched. By pressing the stamp 90 in the first state on the disk 95 covered with an intermediate liquid 96, a substantially uniform force is exerted on the intermediate liquid 96, thereby avoiding the inclusion of air. Figure 15b shows the stamp in a second state wherein the pressing force has increased. Here, the hard basic layer 91 and the hard top layer 93 contact each other to form a single solid body. In the second state, the fluid 94 has flown to a reservoir 97. The fluid 94 may comprise a liquid and/or a gas.

According to a further aspect of the invention, an intermediate liquid is chosen that shrinks during exposure when a high aspect ratio pattern is to be formed. The contact between the liquid and the stamp is mainly along side walls of the stamp. As the resist shrinks during exposure, the hardening liquid is already partially released from the stamp prior to the withdrawal of the stamp. As a result, undesired sticking of the hardened liquid to the stamp is counteracted.

Similarly, according to the invention, an intermediate liquid is chosen that expands during exposure when a low aspect ratio pattern is to be formed. Here, the contact between the liquid and the stamp is mainly on top of the stamp. Consequently, the hardening liquid pushes the stamp already away from the substrate before a withdrawal force is exerted on the stamp. Thereby, undesired sticking of the hardened liquid to the stamp is counteracted.

Optionally, the liquid is exposed at selected locations, e.g. by placing a mask between an exposure source and the stamp. In this way, the light exposure can be adjusted to a desired dose, e.g. depending on an amount of liquid to be hardened.

Preferably, the stamp forms a single solid body so that a homogeneous force can be exerted on the stamp to withdraw is from the substrate, thereby counteracting defects in the realized pattern. In order to further reduce release problems at the stamp, an anti- sticking coating is, according to the invention, applied to the stamp. In addition, according to the invention, the resist is rendered more stiff by adding stiff enhancing material, e.g. nano tubes. As release problems are thus reduced, the yield of the process correspondingly increases. The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

Different aspects of the inventions can be combined or applied independently of each other. As an example, the features according to the invention for enhancing the beam metrology can be applied in combination with multiple beam technology. However, said features for enhancing a beam metrology can also be applied in a system wherein a single beam is generated for exposing a substrate.

Other such variants will be obvious for the person skilled in the art and are considered to lie within the scope of the invention as formulated in the following claims.

Claims

Claims

1. A method of patterning a hard disk medium, comprising the step of applying a lithographic process to a resistive top layer of the hard disk medium, wherein the resistive top layer is exposed to a beam having multiple electron or optical beamlets.

2. A method according to claim 1, wherein foci of the multiple beamlets are arranged at different radial distances from a center point of the hard disk, preferably substantially on a line extending from the center point of the hard disk to an edge of the hard disk.

3. A method according to claim 1 or 2, wherein foci of the multiple beamlets are arranged at different peripheral positions with respect to a center point of the hard disk, preferably substantially on multiple lines extending from the center point of the hard disk to an edge of the hard disk.

4. A method according to any of the previous claims, wherein foci of the multiple beamlets are arranged densely in a two-dimensional segment over the top layer of the hard disk.

5. A method according to any of the previous claims, wherein the number of beamlet foci increases in a radial direction outwardly with respect to the center point of the hard disk.

6. A method according to any of the previous claims, comprising deflecting a beamlet in a radial and/or peripheral direction.

7. A method according to any of the previous claims, comprising the steps of moving a stage supporting the hard disk with a substantially uniform speed in a lateral direction while a beam is deflected stepwise from a first radial deflected position to a second radial deflected position.

8. A method according to any of the previous claims, comprising patterning a ring segment during multiple passes of the respective segment and/or partially overlapping a begin section and an end section of a ring segment to be patterned.

9. A method of patterning a hard disk medium, comprising the step of applying an imprinting process wherein an imprint pattern having a first thickness is realized by application of a stamp having a corresponding pattern and wherein a pattern having a second, larger thickness is realized by application of an etch-technology wherein the imprint pattern functions as a hard mask.

10. A stamp for use in an imprint process for patterning a hard disk medium, comprising a multilayer structure having a hard basic layer, a hard top layer and an intermediate fluid layer sandwiched between the hard basic layer and the hard top layer.

11. An imprint system for patterning hard disk media, comprising imprint tool modules for forming a multiple number of imprint tools serving as parallel production lines for the hard disk media, wherein at least one imprint tool module having a relatively short cycle time is shared by a multiple number of imprint tools.