CA2709718A1

CA2709718A1 - Large area nanopatterning method and apparatus

Info

Publication number: CA2709718A1
Application number: CA2709718A
Authority: CA
Inventors: Boris Kobrin; Igor Landau; Boris Volf
Original assignee: Individual
Current assignee: Rolith Inc
Priority date: 2008-01-22
Filing date: 2008-11-18
Publication date: 2009-07-30
Also published as: TWI518027B; CN105171985A; CN101911249A; AU2008348353A1; KR20110008159A; WO2009094009A1; MX2010007954A; JP5102879B2; EP2238608A4; EP2238608A1; RU2488188C2; TW200932666A; RU2010134893A; JP2011526069A

Abstract

Embodiments of the invention relate to methods and apparatus useful in the nanopatterning of large area substrates, where a rotatable mask is used to image a radiation- sensitive material.
Typically the rotatable mask comprises a cylinder. The nanopatterning technique makes use of Near-Field photolithography, where the mask used to pattern the substrate is in dynamic contact with the substrate. The Near-Field photolithography may make use of an elastomeric phase-shifting mask, or may employ surface plasmon technology, where a rotating cylinder surface comprises metal nano holes or nanoparticles.

Description

1 [00011 LARGE AREA NANOPATTERNING METHOD AND APPARATUS

2 [0002] Field 3 [0003] Embodiments of the invention relate to nanopatterning methods which can be 4 used to pattern large substrates or substrates such as films which may be sold as rolled goods. Other embodiments of the invention pertain to apparatus which may be used to 6 pattern substrates, and which may be used to carry out method embodiments, including 7 the kind described.

8 [0004] Background 9 [0005] This section describes background subject matter related to the disclosed embodiments of the present invention. There is no intention, either express or implied, 11 that the background art discussed in this section legally constitutes prior art.

12 [0006] Nanostructuring is necessary for many present applications and industries and 13 for new technologies which are under development. Improvements in efficiency can be 14 achieved for current applications in areas such as solar cells and LEDs, and in next generation data storage devices, for example and not by way of limitation.

16 [0007] Nanostructured substrates may be fabricated using techniques such as a-beam 17 direct writing, Deep UV lithography, nanosphere lithography, nanoimprint lithography, 18 near-filed phase shift lithography, and plasmonic lithography, for example.

19 [0008] Nanolmprint Lithography (NIL) creates patterns by mechanical deformation of an imprint resist, followed by subsequent processing. The imprint resist is typically a 21 monomeric or polymeric formulation that is cured by heat or by UV light during the 22 imprinting. There are a number of variations of NIL. However, two of the processes 23 appear to be the most important. These are Thermoplastic Nanolmprint Lithography 24 (TNIL) and Step and Flash Nanolmprint Lithography (SFIL).

[0009] TNIL is the earliest and most mature nanoimprint lithography. In a standard 26 TNIL process, a thin layer of imprint resist (a thermoplastic polymer) is spin coated onto a 27 sample substrate. Then a mold, which has predefined topological patterns, is brought into 1 contact with the sample, and pressed against the sample under a given pressure. When 2 heated above the glass transition temperature of the thermoplastic polymer, the pattern on 3 the mold is pressed into a thermoplastic polymer film melt. After the sample with 4 impressed mold is cooled down, the mold is separated from the sample and the imprint resist is left on the sample substrate surface. The pattern does not pass through the 6 imprint resist; there is a residual thickness of unchanged thermoplastic polymer film 7 remaining on the sample substrate surface. A pattern transfer process, such as reactive 8 ion etching, can be used to transfer the pattern in the resist to the underlying substrate.

9 The variation in the residual thickness of unaltered thermoplastic polymer film presents a problem with respect to uniformity and optimization of the etch process used to transfer 11 the pattern to the substrate.

12 [00101 In the SFIL process, a UV curable liquid resist is applied to the sample 13 substrate and the mold is made of a transparent substrate, such as fused silica. After the 14 mold and the sample substrate are pressed together, the resist is cured using UV light, and becomes solid. After separation of the mold from the cured resist material, a similar 16 pattern to that used in TNIL may be used to transfer the pattern to the underlying sample 17 substrate. A number of challenges exist with both the SFIL and TNIL
processes, 18 including template lifetime, throughput rate, imprint layer tolerances, and critical 19 dimension control during transfer of the pattern to the underlying substrate. The residual, non-imprinted layer which remains after the imprinting process requires an additional etch 21 step prior to the main pattern transfer etch. Single field NIL has difficulty in controlling 22 the uniformity of a replicated pattern over a large surface area substrate, due to problems 23 in maintaining a uniform pressure over large areas. A step-and-repeat method can 24 potentially cover large areas, but the microstructure formed in each step is independent from other steps, and the formation of a seamless micro or nanostructure over a large area 26 without stitching is a problem. A stitching error occurs when repeated pattern transfers 27 are not properly aligned.

1 [00111 If a uniformly patterned roller surface can be obtained, roll-to-roll processing 2 might be possible. In a Japanese Unexamined Patent Publication, No.
59200419A, 3 published November 13, 1984, titled "Large Area Exposure Apparatus", Toshio Aoki et 4 al. described the use of a transparent cylindrical drum which can rotate and translate with an internal light source and a film of patterned photomask material attached on the outside 6 of the cylindrical drum. A film of a transparent heat reflective material is present on the 7 inside of the drum. A substrate with an aluminum film on its surface and a photoresist 8 overlying the aluminum film is contacted with the patterned photomask on the drum 9 surface and imaging light is passed through the photomask to image the photoresist on the surface of the aluminum film. The photoresist is subsequently developed, to provide a 11 patterned photoresist. The patterned photoresist is then used as an etch mask for an 12 aluminum film present on the substrate.

13 [00121 There is no description regarding the kinds of materials which were used as a 14 photomask film or as a photoresist on the surface of the aluminum film. A
high pressure mercury lamp light source (500 W) was used to image the photoresist overlying the 16 aluminum film. Glass substrates about 210 mm (8.3 in.) x 150 mm (5.9 in.) and about 17 0.2 mm (0.008 in.) thick were produced using the cylindrical drum pattern transfer 18 apparatus. The feature size of the pattern transferred using the technique was about 500 19 m2, which was apparently a square having a dimension of about 22.2 m x 22.2 m.
This feature size was based on the approximate pixel size of an LCD display at the time 21 the patent application was filed in 1984. The photomask film on the outside of the 22 cylindrical drum was said to last for approximately 140,000 pattern transfers. The contact 23 lithography scheme used by; Toshio Aoki et al. is not capable of producing sub-micron 24 features.

[00131 Tapio Makela et al. of VTT, a technical research center in Finland, have 26 published information about a custom built laboratory scale roll-to-roll imprinting tool 27 dedicated to manufacturing of submicron structures with high throughput.
Hitachi and 1 others have developed a sheet or roll-to-roll prototype NIL machine, and have 2 demonstrated capability to process 15 meter long sheets. The goal has been to create a 3 continuous imprint process using belt molding (nickel plated molds) to imprint 4 polystyrene sheets for large geometry applications such as membranes for fuel cells, batteries and possibly displays. Currently the prototype tools do not offer a desirable 6 throughput. In addition, there is a need to improve reliability and repeatability with 7 respect to the imprinted surface. Toshiba has also published information about a roll-to-8 roll UV-imprinting tool which is said to produce sub-micron feature sizes.

9 [00141 The Nanoimprinting Lithography technique, including the roll-to-roll NIL
still must overcome a number of challenges. Defects can be produced by incomplete 11 filling of negative patterns and the shrinkage phenomenon which often occurs with 12 respect to polymeric materials. Difference in thermal expansion coefficients between the 13 mold and the substrate cause lateral strain, and the strain is concentrated at the corner of 14 the pattern. The strain induces defects and causes fracture defects at the base part of the pattern during the mold releasing step. In addition, the nonuniform thickness of the 16 residual, non-imprinted layer which remains after the imprinting process is particularly 17 harmful in terms of obtaining a uniformly etched pattern into a large area substrate 18 beneath the imprinted resist layer.

19 [00151 Soft lithography is an alternative to photolithography as a method of micro and nano fabrication. This technology relates to replica molding of self assembling 21 monolayers. In soft lithography, an elastomeric stamp with patterned relief structures on 22 its surface is used to generate patterns and structures with feature sizes ranging from 30 23 nm to 100 nm. The most promising soft lithography technique is microcontact printing 24 ( CP) with self-assembled monolayers (SAMS). The basic process of CP
includes: 1.
A polydimethylsiloxane (PDMS) mold is dipped into a solution of a specific material, 26 where the specific material is capable of forming a self-assembled monolayer (SAM).
27 Such specific materials may be referred to as an ink. The specific material sticks to a 1 protruding pattern on the PDMS master surface. 2. The PDMS mold, with the material-2 coated surface facing downward, is contacted with a surface of a metal-coated substrate 3 such as gold or silver, so that only the pattern on the PDMS mold surface contacts the 4 metal-coated substrate. 3. The specific material forms a chemical bond with the metal, so that only the specific material which is on the protruding pattern surface sill remain on the 6 metal-coated surface after removal of the PDMS mold. The specific material forms a 7 SAM on the metal-coated substrate which extends above the metal-coated surface 8 approximately one to two nanometers (just like ink on a piece of paper). 4.
The PDMS
9 mold is removed from the metal-coated surface of the substrate, leaving the patterned SAM on the metal-coated surface.

11 [0016] The best-established specific materials for forming SAMs on gold or silver-12 coated surfaces are alkanethiolates. When the substrate surface contains hydroxyl-13 terminated moieties such as Si/SiO2, Al/A12031 glass, mica, and plasma-treated polymers, 14 alkylsiloxanes work well as the specific materials. With respect to the alkanethiolates, CP of hexadecanethiol on evaporated thin (10 - 200 nm thick) films of gold or silver 16 appears to be the most reproducible process. While these are the best-known materials 17 for carrying out the pattern formation, gold and silver are not compatible with 18 microelectronic devices based on silicon technology, although gold or silver-containing 19 electrodes or conductive wires may used. Currently, CP fo SAMS of siloxanes on Si/SiO2 surfaces are not as tractable as the SAMS of alkanethiolates on gold or silver.
21 The SAMS of siloxanes on Si/Si02 often provide disordered SAMs, and in some cases 22 generate submonolayers or multilayers. Finally, the patterned molds available for CP
23 are flat "stamp" surfaces, and reproducible and reliable printing on large areas not only 24 requires very accurate stitching of the printed pattern from the mold, but also requires constant wetting of the stamp with the SAM-forming specific material, which is quite 26 problematic.

27 [0017] Some new optical lithography techniques based on near field evanescent 1 effects have already demonstrated advantages in printing sub-100 nm structures, though 2 on small areas only. Near-field phase shift lithography NFPSL involves exposure of a 3 photoresist layer to ultraviolet (UV) light that passes through an elastomeric phase mask 4 while the mask is in conformal contact with a photoresist. Bringing an elastomeric phase mask into contact with a thin layer of photoresist causes the photoresist to "wet" the 6 surface of the contact surface of the mask. Passing UV light through the mask while it is 7 in contact with the photoresist exposes the photoresist to the distribution of light intensity 8 that develops at the surface of the mask. In the case of a mask with a depth of relief that 9 is designed to modulate the phase of the transmitted light by in , a local null in the intensity appears at the step edge of relief. When a positive photoresist is used, exposure 11 through such a mask, followed by development, yields a line of photoresist with a width 12 equal to the characteristic width of the null in intensity. For 365 nm (Near UV) light in 13 combination with a conventional photoresist, the width of the null in intensity is 14 approximately 100 nm. A PDMS mask can be used to form a conformal, atomic scale contact with a flat, solid layer of photoresist. This contact is established spontaneously 16 upon contact, without applied pressure. Generalized adhesion forces guide this process 17 and provide a simple and convenient method of aligning the mask in an angle and 18 position in the direction normal to the photoresist surface, to establish perfect contact.

19 There is no physical gap with respect to the photoresist. PDMS is transparent to UV light with wavelengths greater than 300 nm. Passing light from a mercury lamp (where the 21 main spectral lines are at 355 - 365 nm) through the PDMS while it is in conformal 22 contact with a layer of photoresist exposes the photoresist to the intensity distribution that 23 forms at the mask.

24 [00181 Yasuhisa Inao, in a presentation entitled "Near-Field Lithography as a prototype nano-fabri cation tool", at the 32nd International Conference on Micro and Nano 26 Engineering in 2006, described a step-and-repeat near-field nanolithography developed by 27 Canon, Inc. Near-field lithography (NFL) is used, where the distance between a mask and 1 the photoresist to which a pattern is to be transferred are as close as possible. The initial 2 distance between the mask and a wafer substrate was set at about 50 m. The patterning 3 technique was described as a "tri-layer resist process", using a very thin photoresist. A

4 pattern transfer mask was attached to the bottom of a pressure vessel and pressurized to accomplish a "perfect physical contact" between the mask and a wafer surface.
The mask 6 was "deformed to fit to the wafer". The initial 50 m distance between the mask and the 7 wafer is said to allows movement of the mask to another position for exposure and 8 patterning of areas more than 5 mm x 5mm. The patterning system made use of i-line 9 (365 nm) radiation from a mercury lamp as a light source. A successful patterning of a 4 inch silicon wafer with structures smaller than 50 nm was accomplished by such a step-11 and-repeat method.

12 [00191 In an article entitled "Large-area patterning of 50 nm structures on flexible 13 substrates using near-field 193 nm radiation", JVST B 21 (2002), at pages 78 - 81, Kunz 14 et al. applied near-field phase shift mask lithography to the nanopatterning of flexible sheets (Polyimide films) using rigid fused silica masks and deep UV wavelength 16 exposure. In a subsequent article entitled "Experimental and computational studies of 17 phase shift lithography with binary elastomeric masks", JVST B 24(2) (2006) at pages 18 828 - 835, Maria et al. present experimental and computational studies of a phase shifting 19 photolithographic technique that uses binary elastomeric phase masks in conformal contact with layers of photoresist. The work incorporates optimized masks formed by 21 casting and curing prepolymers to the elastomer poly(dimethylsiloxane) against 22 anisotropically etched structures of single crystal silicon on Si02/Si. The authors report 23 on the capability of using the PDMS phase mask to form resist features in the overall 24 geometry of the relief on the mask.

[00201 U.S. Patent No. 6,753,131 to Rogers et al, issued June 22, 2004, titled 26 "Transparent Elastomeric, Contact-Mode Photolithography Mask, Sensor, and Wavefront 27 Engineering Element", describes a contact-mode photolithography phase mask which 1 includes a diffracting surface having a plurality of indentations and protrusions. The 2 protrusions are brought into contact with a surface of a positive photoresist, and the 3 surface is exposed to electromagnetic radiation through the phase shifting mask. The 4 phase shift due to radiation passing through indentations as opposed to the protrusions is essentially complete. Minima in intensity of electromagnetic radiation are thereby 6 produced at boundaries between the indentations and protrusions. The elastomeric mask 7 conforms well to the surface of the photoresist, and following development of the 8 photoresist, features smaller than 100 nm can be obtained. (Abstract) In one embodiment, 9 reflective plates are used exterior to the substrate and the contact mask, so radiation will be bounced to a desired location at a shifted phase. In another embodiment, the substrate 11 may be shaped in a manner which causes a deformation of the phase shifting mask, 12 affecting the behavior of the phase shifting mask during exposure.

13 [0021] U.S. Patent Application Publication No. U.S. 2006/0286488, of Rogers et 14 al., published December 21, 2006, titled "Methods And Devices For Fabricating Three-Dimensional Nanoscale Structures", describes methods of fabricating 3-D
structures on 16 substrate surfaces. The 3-D structures may be generated using a conformable, elastomeric 17 phase mask capable of conformal contact with a radiation sensitive material undergoing 18 photo processing (to produce the 3-D structures). The 3D structures may not extend 19 entirely through the radiation sensitive material. (Abstract) [0022] Near Field Surface Plasmon Lithography (NFSPL) makes use of near-field 21 excitation to induce photochemical or photophysical changes to produce nanostructures.
22 The main near-field technique is based on the local field enhancement around metal 23 nanostructures when illuminated at the surface plasmon resonance frequency.
Plasmon 24 printing consists of the use of plasmon guided evanescent waves through metallic nanostructures to produce photochemical and photophysical changes in a layer below the 26 metallic structure. In particular, visible exposure (,X = 410 nm) of silver nanoparticles in 27 close proximity to a thin film of a g-line photoresist (AZ- 1813 available from AZ-1 Electronic Materials, MicroChemicals GmbH, Ulm, Germany) can produce selectively 2 exposed areas with a diameter smaller than A/20. W. Srituravanich et al. in an article 3 entitled "Plasmonic Nanolithography", Nanoletters V4, N6 (2004), pp. 1085 -1088, 4 describes the use of near UV light ( A = 230 nm - 350 nm) to excite SPs on a metal substrate, to enhance the transmission through subwavelength periodic apertures with 6 effectively shorter wavelengths compared to the excitation light wavelength.
A

7 plasmonic mask designed for lithography in the UV range is composed of an aluminum 8 layer perforated with 2 dimensional periodic hole arrays and two surrounding dielectric 9 layers, one on each side. Aluminum is chosen since it can excite the SPs in the UV range.
Quartz is employed as the mask support substrate, with a poly(methyl methacrylate) 11 spacer layer which acts as adhesive for the aluminum foil and as a dielectric between the 12 aluminum and the quartz. Poly(methyl methacrylate) is used in combination with quartz, 13 because their transparency to UV light at the exposure wavelength (i-line at 365 nm) and 14 comparable dielectric constants (2.18 and 2.30, quartz and PMMA, respectively). A sub-100 rim dot array pattern on a 170 nm period has been successfully generated using an 16 exposure radiation of 365 nm wavelength. Apparently the total area of patterning was 17 about 5 m x 5 m, with no scalability issues discussed in the paper.

18 [00231 It does not appear that an imprinting method (thermal or UV-cured) or soft 19 lithography using printing with SAM materials are highly manufacturable processes. In general, the imprinting method creates deformation of the substrate material due to the 21 thermal treatment (thermal NIL, for example) or shrinkage of pattern features upon 22 polymer curing (UV-cured polymeric features). Moreover, due to the application of 23 pressure (hard contact) between a stamp and a substrate, defects are essentially 24 unavoidable, and a stamp has a very limited lifetime. Soft lithography does have an advantage in that it is thermal and stress-free printing technology. However, the use of a 26 SAM as an "ink" for a sub-100 nm pattern is very problematic due to the drifting of 27 molecules over the surface, and application over large areas has not been proved 1 experimentally.

2 [00241 SUMMARY

3 [00251 Embodiments of the invention pertain to methods and apparatus useful in the 4 nanopatterning of large area substrates ranging from about 200 mm2 to about 1,000,000 mm 2, by way of example and not by way of limitation. In some instances the substrate 6 may be a film, which has a given width and an undefined length, which is sold on a roll.
7 The nanopatterning technique makes use of Near-Field UV photolithography, where the 8 mask used to pattern the substrate is in dynamic contact or in very close proximity (in the 9 evanescent field, less than 100 nm) from the substrate. The Near-Field photolithography may include a phase-shifting mask or surface plasmon technology. The feature size 11 obtainable using the methods described ranges from about 1 gm down to about 1 nm, and 12 frequently ranges from about 100 nm down to about 10 nm.

13 [00261 One embodiment the exposure apparatus which includes a phase-shifting 14 mask in the form of a UV-transparent rotatable mask having specific phase shifting relief on it's outer surface. In another embodiment of the phase-shifting mask technology, the 16 transparent rotatable mask, which is typically a cylinder, may have a polymeric film 17 which is the phase-shifting mask, and the mask is attached to the cylinder's outer surface.
18 When it is difficult to obtain good and uniform contact with the substrate surface, 19 especially for large processing areas, it is advantageous to have the polymeric film be a conformal, elastomeric polymeric film such as PMDS, which makes excellent conformal 21 contact with the substrate through Van-der Waals forces. The polymeric film phase-22 shifting mask may consist of multiple layers, where the outer layer is nanopatterned to 23 more precisely represent prescribed feature dimensions in a radiation-sensitive 24 (photosensitive) layer.

[00271 Another embodiment of the exposure apparatus employs a soft elastomeric 26 photomask material, such as a PDMS film, having non-transparent features fabricated on 1 one of it's surfaces, which is attached to the outer surface of the cylinder. Such features 2 may be chrome features produced on the PDMS film using one of the lithographic 3 techniques known in the art.

4 [00281 In an embodiment of the exposure apparatus which includes surface plasmon technology, a metal layer or film is laminated or deposited onto the outer surface of the 6 rotatable mask, which is typically a transparent cylinder. The metal layer or film has a 7 specific series of through nanoholes. In another embodiment of the surface plasmon 8 technology, a layer of metal nanoparticles is deposited on the transparent rotatable mask's 9 outer surface, to achieve the surface plasmons enhanced nanopatterning. A
radiation source is provided interior to the transparent cylinder. For example, and not by way of 11 limitation, a UV lamp may be installed interior of the cylinder. In the alternative, the 12 radiation source may be placed outside the cylinder, with light from the radiation source 13 being piped to the interior of the cylinder through one or both ends of the cylinder. The 14 radiation may be directed from outside the cylinder or within the cylinder toward particular areas within the interior of the cylinder using an optical system including 16 mirrors, lenses, or combinations thereof, for example. Radiation present within the 17 cylinder may be directed toward the mask substrate contact area using an optical grating.
18 The radiation may be directed toward the mask substrate area (coupled) through a 19 waveguide with a grating. The waveguide or grating is typically placed inside the cylinder, to redirect radiation toward the contact areas between the cylinder outer surface 21 and the substrate surface to be imaged.

22 [00291 In a specialized embodiment of a light source of radiation, an OLED
flexible 23 display may be attached around the exterior of the rotatable mask, to emit light from each 24 of the pixels toward the substrate. In this instance the rotatable mask does not need to be transparent. In addition, the particular pattern to be transferred to a radiation-sensitive 26 material on the substrate surface may be generated depending on the application, through 27 control of the light emitted from the OLED. The pattern to be transferred may be changed 1 "on the fly" without the need to shut down the manufacturing line.

2 [00301 To provide high throughput of pattern transfer to a radiation-sensitive 3 material, and increase the quantity of nanopatterned surface area, it is helpful to move the 4 substrate or the rotatable mask, such as a cylinder, against each other. The cylinder is rotated on the substrate surface when the substrate is static or the substrate is moved 6 toward the cylinder while the cylinder is static. For reasons discussed below, there are 7 advantages to moving the substrate toward the cylinder.

8 [00311 It is important to be able to control the amount of force which occurs at the 9 contact line between the cylinder and the radiation-sensitive material on the surface of the substrate (for example the contact line between an elastomeric nanopatterned film present 11 on the surface of the cylinder and a photoresist on the substrate surface).
To control this 12 contact line, the cylinder may be supported by a tensioning device, such as, for example, 13 springs which compensate for the cylinder's weight. The substrate or cylinder (or both) 14 are moved (upward and downward) toward each other, so that a spacing between the surfaces is reduced, until contact is made between the cylinder surface and the radiation-16 sensitive material (the elastomeric nanopatterned film and the photoresist on the substrate 17 surface, for example). The elastomeric nanopatterned film will create a bond with a 18 photoresist via Van-der Walls forces. The substrate position is then moved back 19 (downward) to a position at which the springs are elongated, but the elastomeric nanopatterned film remains in contact with the photoresist. The substrate may then be 21 moved toward the cylinder, forcing the cylinder to rotate, maintaining a dynamic contact 22 between the elastomeric nanopatterned film and the photoresist on the substrate surface.
23 alternatively, the cylinder can be rotated and the substrate can be moved independently, 24 but in synchronous motion, which will assure slip-free contact during dynamic exposure.
[00321 Multiple cylinders may be combined into one system and arranged to expose 26 the radiation-sensitive surface of the substrate in a sequential mode, to provide double, 27 triple, and multiple patterning of the substrate surface. This exposure technique can be 1 used to provide higher resolution. The relative positions of the cylinders may be 2 controlled by interferometer and an appropriate computerized control system.

3 [0033] In another embodiment, the exposure dose may affect the lithography, so that 4 an edge lithography (where narrow features can be formed, which corresponds to a shift of phase in a PDMS mask, for example) can be changed to a conventional contact 6 lithography, and the feature size in an imaged photoresist can be controlled by exposure 7 dose. Such control of the exposure dose is possible by controlling the radiation source 8 power or the rotational speed of the cylinder (exposure time). The feature size produced 9 in the photoresist may also be controlled by changing the wavelength of the exposure radiation, light source, for example.

11 [0034] The masks on the cylinders may be oriented by an angle to the direction of 12 substrate movement. This enables pattern formation in different directions against the 13 substrate. Two or more cylinders can be placed in sequence to enable 2D
patterns.

14 [0035] In another embodiment, the transparent cylindrical chamber need not be rigid, but may be formed from a flexible material which may be pressurized with an 16 optically transparent gas. The mask may be the cylinder wall or may be a conformal 17 material present on the surface of the cylinder wall. This permits the cylinder to be rolled 18 upon a substrate which is not flat, while making conformal contact with the substrate 19 surface.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

21 [0037] So that the manner in which the exemplary embodiments of the present 22 invention are attained is clear and can be understood in detail, with reference to the 23 particular description provided above, and with reference to the detailed description of 24 exemplary embodiments, applicants have provided illustrating drawings. It is to be appreciated that drawings are provided only when necessary to understand exemplary 26 embodiments of the invention and that certain well known processes and apparatus are 1 not illustrated herein in order not to obscure the inventive nature of the subject matter of 2 the disclosure.

3 [0038] Figure 1 A shows a cross-sectional view of one embodiment of an apparatus 4 100 useful in patterning of large areas of substrate material, where a radiation transparent cylinder 106 has a hollow interior 104 in which a radiation source 102 resides. In this 6 embodiment, the exterior surface 111 of the cylinder 106 is patterned with a specific 7 surface relief 112. The cylinder 106 rolls over a radiation sensitive material 108 which 8 overlies a substrate 110.

9 [0039] Figure 1 B shows a top view of the apparatus and substrate illustrated in Figure 1 A, where the radiation sensitive material 108 has been imaged 109 by radiation 11 (not shown) passing through surface relief 112.

12 [0040] Figure 2 shows a cross-sectional view of another embodiment of an 13 apparatus 200 useful in patterning of large areas of substrate material. In Figure 2, the 14 substrate is a film 208 upon which a pattern is imaged by radiation which passes through surface relief 212 on a first (transparent) cylinder 206 while film 208 travels from roll 211 16 to roll 213. A second cylinder 215 is provided on the backside 209 of film 208 to control 17 the contact between the film 208 and the first cylinder 206.

18 [0041] Figure 3 shows a cross-sectional view of another embodiment of an 19 apparatus 300 useful in patterning large areas of substrate material. In Figure 3, the substrate is a film 308 which travels from roll 311 to roll 313. A first transparent cylinder 21 306 with surface relief 312 is used to pattern the topside 310 of film 308, while a second 22 transparent cylinder 326 with surface relief 332 is used to pattern the bottom side 309 of 23 film 308.

1 [0042] Figure 4A shows a cross-sectional view of an embodiment 400 of a 2 transparent cylinder 406 which includes a hollow center area 404 with an internal source 3 of radiation 402. The surface relief area 412 is a conformal structure which includes 4 polymer film 415 with a patterned surface 413 which is particularly useful for near-field lithography.

6 [0043] Figure 4B shows an enlargement of surface 413, which is a surface relief 7 polymer structure 413 on top of polymeric base material 415. In Figure 4B, the polymer 8 base material 415 may be either the same polymeric material or may be a different 9 polymeric material from the patterned surface material 413.

[0044] Figure 5A shows a cross sectional view of an alternative embodiment 500 of 11 surface relief 512 which is present on a hollow transparent cylinder 506.

12 [0045] Figure 5B shows an enlargement of the surface relief 512, which is a thin 13 metal layer 514 which is patterned with a series of nanoholes 513, where the metal layer 14 is applied over the exterior surface 511 of hollow transparent cylinder 506.

[0046] Figure 5C shows an alternative surface relief 522 which may be used on the 16 surface of transparent cylinder 506. Surface relief 522 is formed by metal particles 526 17 which may be applied directly upon the exterior surface 511 of hollow transparent 18 cylinder 506 or may be applied on a transparent film 524 which is attached to the exterior 19 surface 511 of hollow transparent cylinder 506.

[0047] Figure 6A is a schematic three dimensional illustration 600 of a transparent 21 cylinder 604 having a patterned surface 608, where the cylinder 604 is suspended above a 22 substrate 610 using a tensioning device 602 illustrated as springs..

1 [0048] Figure 6B is a schematic of an embodiment 620 where the radiation used to 2 accomplish imaging is supplied from a radiation source 612 exterior to cylinder 604, with 3 the radiation distributed internally 615 and 616 within the hollow portion of the cylinder 4 604.

[0049] Figure 6C is a schematic of an embodiment 630 where the radiation used to 6 accomplish imaging is supplied from the exterior radiation source 612 is focused 617 7 into a waveguide 618 and distributed from the waveguide 618 to an optical grating 621 8 present on the interior surface 601 of the cylinder 604.

9 [0050] Figure 6D is a schematic of an embodiment 640 where the radiation used to accomplish imaging is supplied from two exterior radiation sources 612A and 612B, and 11 is focused 621 and 619, respectively upon an optical grating 621 present on the interior 12 surface 601 of cylinder 604.

13 [0051] Figure 7A is a schematic showing the use of multiple cylinders, such as two 14 cylinders 702 and 704, for example, in series to provide multiple patterning, which may be used to obtain higher resolution, for example.

16 [0052] Figure 7B is a cross-sectional schematic showing a pattern 706 created by a 17 first cylinder 702 after imaging and development of a radiation-sensitive material 710.
18 The altered pattern 708 is after imaging and development of the radiation-sensitive 19 material 710 where the altered pattern 708 is created by use of the first cylinder 702 in combination with a second cylinder 704.

21 [0053] Figure 8 shows a cross-sectional schematic of a deformable cylinder 800, the 22 interior 804 of which is pressurized using an apparatus 813 which supplies an optically 1 transparent gas. The outer surface 811 of deformable cylinder 800 may be a 2 nanopatterned/nanostructured film 802 of a conformable material, which can be rolled 3 upon a non-flat substrate 805 so that radiation from radiation source 802 can be precisely 4 applied over a surface 816 of substrate 805.

[0054] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

6 [0055] As a preface to the detailed description, it should be noted that, as used in this 7 specification and the appended claims, the singular forms "a", "an", and "the" include 8 plural referents, unless the context clearly dictates otherwise.

9 [0056] When the word "about" is used herein, this is intended to mean that the nominal value presented is precise within 10 %.

11 [0057] Embodiments of the invention relate to methods and apparatus useful in the 12 nanopatterning of large area substrates, where a rotatable mask is used to image a 13 radiation-sensitive material. Typically the rotatable mask comprises a cylinder. The 14 nanopatterning technique makes use of near-field photolithography, where the wavelength of radiation used to image a radiation-sensitive layer on a substrate is 438 nm or less, and 16 where the mask used to pattern the substrate is in contact with the substrate. The near-17 field photolithography may make use of a phase-shifting mask, or nanoparticles on the 18 surface of a transparent rotating cylinder, or may employ surface plasmon technology, 19 where a metal layer on the rotating cylinder surface comprises nano holes.
The detailed description provided below is just a sampling of the possibilities which will be recognized 21 by one skilled in the art upon reading the disclosure herein.

22 [0058] Although the rotating mask used to generate a nanopattern within a layer of 23 radiation-sensitive material may be of any configuration which is beneficial, and a 24 number of these are described below, a hollow cylinder is particularly advantageous in terms of imaged substrate manufacturability at minimal maintenance costs.
Figure 1A

26 shows a cross-sectional view of one embodiment of an apparatus 100 useful in patterning 1 of large areas of substrate material, where a radiation transparent cylinder 106 has a 2 hollow interior 104 in which a radiation source 102 resides. In this embodiment, the 3 exterior surface 111 of the cylinder 106 is patterned with a specific surface relief 112.
4 The cylinder 106 rolls over a radiation sensitive material 108 which overlies a substrate 110. Figure 1B shows a top view of the apparatus and substrate illustrated in Figure 1 A, 6 where the radiation sensitive material 108 has been imaged 109 by radiation (not shown) 7 passing through surface relief 112. The cylinder is rotating in the direction shown by 8 arrow 118, and radiation from a radiation source 102 passes through the nanopattern 112 9 present on the exterior surface 103 of rotating cylinder 106 to image the radiation-sensitive layer (not shown) on substrate 108, providing an imaged pattern 109 within the 11 radiation-sensitive layer. The radiation-sensitive layer is subsequently developed to 12 provide a nanostructure on the surface of substrate 108. In Figure 1B, the rotatable 13 cylinder 106 and the substrate 120 are shown to be independently driven relative to each 14 other. In another embodiment, the substrate 120 may be kept in dynamic contact with a rotatable cylinder 106 and moved in a direction toward or away from a contact surface of 16 the rotatable cylinder 106 to provide motion to an otherwise static rotatable cylinder 106.
17 In yet another embodiment, the rotatable cylinder 106 may be rotated on a substrate 120 18 while the substrate is static.

19 [0059] The specific surface relief 112 may be etched into the exterior surface of the transparent rotating cylinder 106. In the alternative, the specific surface relief 112 may be 21 present on a film of polymeric material which is adhered to the exterior surface of rotating 22 cylinder 106. The film of polymeric material may be produced by deposition of a 23 polymeric material onto a mold (master). The master, created on a silicon substrate, for 24 example, is typically generated using an e-beam direct writing of a pattern into a photoresist present on the silicon substrate. Subsequently the pattern is etched into the 26 silicon substrate. The pattern on the silicon master mold is then replicated into the 27 polymeric material deposited on the surface of the mold. The polymeric material is 1 preferably a conformal material, which exhibits sufficient rigidity to wear well when used 2 as a contact mask against a substrate, but which also can make excellent contact with the 3 radiation-sensitive material on the substrate surface. One example of the conformal 4 materials generally used as a transfer masking material is PDMS, which can be cast upon the master mold surface, cured with UV radiation, and peeled from the mold to produce 6 excellent replication of the mold surface.

7 [00601 Figure 2 shows a cross-sectional view 200 of another embodiment of an 8 apparatus 200 useful in patterning of large areas of substrate material. In Figure 2, the 9 substrate is a film 208 upon which a pattern is imaged by radiation which passes through surface relief 212 on a first (transparent) cylinder 206 while film 208 travels from roll 211 11 to roll 213. A second cylinder 215 is provided on the backside 209 of film 208 to control 12 the contact between the film 208 and the first cylinder 206. The radiation source 202 13 which is present in the hollow space 204 within transparent cylinder 206 may be a 14 mercury vapor lamp or another radiation source which provides a radiation wavelength of 365 nm or less. The surface relief 212 may be a phase-shift mask, for example, where 16 the mask includes a diffracting surface having a plurality of indentations and protrusions, 17 as discussed above in the Background Art. The protrusions are brought into contact with 18 a surface of a positive photoresist ( a radiation-sensitive material), and the surface is 19 exposed to electromagnetic radiation through the phase mask. The phase shift due to radiation passing through indentations as opposed to the protrusions is essentially 21 complete. Minima in intensity of electromagnetic radiation are thereby produced at 22 boundaries between the indentations and protrusions. An elastomeric phase mask 23 conforms well to the surface of the photoresist, and following development of the 24 photoresist, features smaller than 100 nm can be obtained [00611 Figure 3 shows a cross-sectional view 300 of another embodiment of an 26 apparatus 300 useful in patterning large areas of substrate material. The substrate is a 27 film 308 which travels from roll 311 to roll 313. There is a layer of radiation-sensitive I material (not shown) on both the topside 310 of film 308 and the bottom side 309 of film 2 308. There is a first transparent cylinder 306, with a hollow center 304, which includes a 3 radiation source 302, having surface relief 312, which is used to pattern the top side 310 4 of film 308. There is a second transparent cylinder 326, with a hollow center 324, which includes a radiation source 322, having surface relief 332, which is used to pattern the 6 bottom side 309 of film 308.

7 [00621 Figure 4A shows a cross-sectional view 400 of an embodiment of a 8 transparent cylinder 406 which includes a hollow center area 404 with an internal source 9 of radiation 402. The surface relief 412 is a conformal structure which includes polymer film 415 with a patterned surface 413 which is particularly useful for near-field 11 lithography. The polymeric material of patterned surface 413 needs to be sufficiently 12 rigid that the pattern will contact a substrate surface to be imaged in the proper location.
13 At the same time, the polymeric material must conform to the surface of a radiation-14 sensitive material (not shown) which is to be imaged.

[00631 Figure 4B shows an enlargement of surface 413, which is a surface relief 16 polymer structure 413 on top of polymeric base material 415. In Figure 4B, the polymer 17 base material 415 may be either the same polymeric material or may be a different 18 polymeric material from the patterned surface material 413. A transparent conformal 19 material such as a silicone or PDMS, for example, may be used as polymer film 415, in combination with a more rigid transparent overlying layer of material, such as PDMS with 21 a different ratio of mixing components, or polymethyl methacrylate PMMA, for example.
22 This provides a patterned surface 413, which helps avoid distortion of features upon 23 contact with a location on the radiation-sensitive surface of a substrate (not shown), while 24 the polymeric base material simultaneously provides conformance with the substrate surface in general.

26 [00641 Figure 5A shows a cross sectional view 500 of a transparent cylinder 506, 27 with hollow central area 504 including a radiation source 502, where the surface 511 1 presents an alternative embodiment of surface relief 512. Figure 5B shows an 2 enlargement of the surface relief 512, which is a thin metal layer 514 which is patterned 3 with a series of nanoholes 513, where the metal layer is present on the exterior surface 4 511 of hollow transparent cylinder 506. The metal layer may be a patterned layer adhered to the exterior surface of transparent cylinder 506. In the alternative, a metal layer may be 6 deposited on the surface of the transparent cylinder by evaporation or sputtering or 7 another technique known in the art and then may subsequently etched or ablated with a 8 laser to provide a patterned metal exterior surface 511. Figure 5C shows an alternative 9 surface relief 522 which may be used on the surface of transparent cylinder 506. Surface relief 522 is formed by metal particles 526 which are applied on an exterior surface 511 of 11 hollow transparent cylinder 506, or on a transparent film 524 which is attached to the 12 exterior surface 511 of hollow transparent cylinder 506.

13 [0065] Figure 6A is a schematic three dimensional illustration 600 of a transparent 14 cylinder 604 having a patterned surface 608. A radiation source (not shown) is present within the interior of transparent cylinder 604. The transparent cylinder 604 is suspended 16 above a substrate 610 using a tensioning device 602, which is shown as springs in 17 illustration 600. One of skill in the art of mechanical engineering will be familiar with a 18 number of tensioning devices which may be used to obtain the proper amount of contact 19 between the outer surface 608 of transparent cylinder 604 and the surface of substrate 610. In one embodiment method of using the apparatus shown in Figure 6A, the 21 apparatus is used to image a radiation-sensitive material (not shown) on a substrate 610, 22 where substrate 610 is a polymeric film, which may be supplied and retrieved on a roll to 23 roll system of the kind shown in Figure 2. The transparent cylinder 604 is lowered toward 24 the polymeric film substrate (or the polymeric film substrate is raised), until contact is made with the radiation-sensitive material. The polymeric film, which is typically 26 elastomeric will create a Van-der-Walls force bond with the radiation-sensitive material.
27 The transparent cylinder 604 may then be raised (or the polymeric film substrate lowered) 1 to a position where contact remains between the surface 608 of transparent cylinder 604 2 and the surface of the radiation-sensitive material, but the tension between the two 3 surfaces is such that the force placed on the surface 608 is minimal. This enables the use 4 of very fine nanopatterned features on the surface 608 of transparent cylinder 604. When the substrate 610 begins to move, the transparent cylinder 604 will also move, forcing 6 transparent cylinder 604 to rotate, maintaining the dynamic contact between the radiation-7 sensitive material and the underlying polymeric film substrate 610. At any moment of the 8 dynamic exposure, the contact between the cylinder and a photosensitive layer is limited 9 to one narrow line. Due to strong Van-der Walls forces between an elastomeric film, for example, on the cylinder exterior surface and the radiation sensitive (photo sensitive) 11 layer on the substrate, contact is maintained uniform throughout the entire process, and 12 along the entire width of the mask (length) on the cylinder surface. In instances where 13 Van-der-Walls forces do not provide a strong enough adhesion between the cylinder 14 contact surface and a photosensitive layer, an actuating (rotating) cylinder using a stepper-motor synchronized with the translational movement of the substrate may be used. This 16 provides a slip-free exposure process for polymeric or other cylinder surface material 17 which does not provide strong adhesion forces relative to the substrate.

18 [00661 Figure 6B is a schematic of an embodiment 620 where the radiation used to 19 accomplish imaging is supplied from a radiation source 612 exterior to cylinder 604, with the radiation distributed internally 615 and 616 within the hollow portion of the cylinder 21 604. The radiation may be directed through the transparent cylinder 604 through the 22 patterned mask surface 608 toward the radiation-sensitive surface (not shown) of 23 substrate 608 using various lenses, mirrors, and combinations thereof.

24 [00671 Figure 6C is a schematic of an embodiment 630 where the radiation used to accomplish imaging of the radiation-sensitive material is supplied from a location which 26 is exterior to the transparent cylinder 604. The exterior radiation source 612 is focused 27 617 into a waveguide 618 and distributed from the waveguide 618 to an optical grating 1 620 present on the interior surface 601 of the cylinder 604.

2 [0068] Figure 6D is a schematic of an embodiment 640 where the radiation used to 3 accomplish imaging is supplied from two exterior radiation sources 612A and 612B, and 4 is focused 621 and 619, respectively, upon an optical grating 620 present on the interior surface 601 of cylinder 604.

6 [0069] Figure 7A is a schematic 700 showing the use of multiple cylinders, such as 7 two cylinders 702 and 704, for example, in series to provide multiple patterning, which 8 may be used to obtain higher resolution, for example. The relative positions of the 9 cylinders 702 and 704, for example may be controlled using data from an interferometer (not shown) in combination with a computerized control system (not shown).

11 [0070] Figure 7B is a cross-sectional schematic 720 showing a pattern 706 created 12 by a first cylinder 702 after imaging and development of a radiation-sensitive material 13 710. The altered pattern 708 is after imaging and development of the radiation-sensitive 14 material 710 where the altered pattern 708 is created by use of the first cylinder 702 in combination with a second cylinder 704.

16 [0071] Figure 8 shows a cross-sectional schematic of a deformable cylinder 800, the 17 interior 804 of which is pressurized using an apparatus 813 which supplies an optically 18 transparent gas, such as nitrogen, for example. The outer surface 811 of deformable 19 cylinder 800 may be a nanopatterned/nanostructured film 812 of a conformable material, which can be rolled upon a non-flat substrate 805 so that radiation from radiation source 21 802 can be precisely applied over a surface 816 of substrate 805.

22 [0072] In another embodiment, a liquid having a refractive index of greater than one 23 may be used between the cylinder surface and a radiation sensitive (photo sensitive, for 24 example) material present on the substrate surface. Water may be used, for example.

This enhances the pattern feature's contrast in the photosensitive layer.

26 [0073] While the invention has been described in detail for a variety of 27 embodiments above, various modifications within the scope and spirit of the invention 1 will be apparent to those of working skill in this technological field.
Accordingly, the 2 scope of the invention should be measured by the appended claims.

Claims

1. A method of near-field nanolithography comprising:

a) providing a substrate having a radiation-sensitive layer on said substrate surface;

b) providing a rotatable mask having a nanopattern on an exterior surface of said rotatable mask;

c) contacting said nanopattern with said radiation-sensitive layer on said substrate surface;

d) distributing radiation through said nanopattern, while rotating said rotatable mask over said radiation-sensitive layer, whereby an image having a feature size ranging from less than 1 µm down to about 1 nm is created in said radiation-sensitive layer.

2. A method in accordance with Claim 1, wherein said feature size ranges from about 100 nm down to about 10 nm.

3. A method in accordance with Clam 1, wherein said radiation has a wavelength of 436 nm or less.

4 A method in accordance with Claim 1, wherein said nanopattern is a conformable nanopattern, which conforms to said radiation-sensitive layer on said substrate surface.

5. A method in accordance with Claim 4, wherein said conformable nanopattern is a shaped or nanostructured polymeric material.

6. A method in accordance with Claim 3, wherein said rotatable mask is a phase-shifting mask which causes radiation to form an interference pattern in said radiation-sensitive layer.

7. A method in accordance with Claim 3, wherein said mask employs surface plasmon behavior.

8. A method in accordance with Claim 1, wherein said rotatable mask is a cylinder.

9. A method in accordance with Claim 8, wherein said cylinder has a flexible wall, whereby said cylindrical shape may be deformed upon contact with said substrate surface.

10. A method in accordance with Claim 9, wherein an optically transparent gas is used to fill said cylinder.

11. A method in accordance with Claim 3, wherein said rotatable mask is a transparent cylinder, whereby radiation may be transmitted from a location interior of said cylinder.

12. A method in accordance with Claim 11, wherein said mask is a phase shifting mask which is present as a relief on a surface of said transparent cylinder.

13. A method in accordance with Claim 11, wherein said mask is a phase shifting mask which is present on a layer applied over a surface of said cylinder.

14. A method in accordance with Claim 13, wherein said phase shifting mask consists of multiple layers, and the outer layer is nanopatterned to more precisely represent prescribed feature dimensions in said photosensitive layer.

15. A method in accordance with Claim 8, wherein said substrate is kept in dynamic contact with said rotatable cylinder and moved in a direction toward or away from a contact surface of said rotatable cylinder during distribution of radiation from said contact surface of said cylinder.

16. A method in accordance with Claim 8, wherein said cylinder is rotated on said substrate while said substrate is static.

17. A method in accordance with any one of Claim 1 through Claim 16, wherein multiple rotating masks are contacted with a radiation-sensitive layer.

18. A method in accordance with Claim 1, wherein said rotatable mask and said substrate surface are moved independently using a stepper-motor and a motorized substrate translational mechanism, and wherein movement of said rotatable mask and said substrate surface are synchronized with each other, whereby a slip-free contact exposure of said radiation-sensitive layer is achieved.

19. A method in accordance with Claim 1 or Claim 18, wherein a liquid is supplied to an interface between said rotatable mask and said substrate surface.

20. An apparatus to carry out near-field lithography, comprising:

a) a rotatable mask having a nanopattern on an exterior surface of said mask;
and b) a radiation source which supplies radiation of a wavelength of 436 nm or less from said nanopattern, while said nanopattern is in contact with a radiation-sensitive layer of material.

21. An apparatus in accordance with Claim 20, wherein said rotatable mask is transparent.

22. An apparatus in accordance with Claim 21, wherein said rotatable mask is a phase-shifting mask.

23. An apparatus in accordance with Claim 21, wherein said rotatable mask employs radiation generated using surface plasmon techniques.

24. An apparatus in accordance with Claim 22, wherein a surface of said mask comprises a metal layer including nanoholes.

25. An apparatus in accordance with any one of Claim 20 through Claim 24, wherein said rotatable mask is a cylinder.

26. An apparatus in accordance with Claim 25, wherein said cylinder is a flexible cylinder.

27. An apparatus in accordance with Claim 26, wherein said flexible cylinder is filled with an optically transparent gas.

28. An apparatus in accordance with Claim 25, wherein multiple cylinders are present in an arrangement so that said multiple cylinders pass over a substrate in sequence.

29. An apparatus in accordance with Claim 25, wherein multiple cylinders are present, and wherein a cylinder is present on both the top side and bottom side of a substrate which is imaged by said apparatus.

30. An apparatus in accordance with Claim 29, wherein at least one cylinder which transmits imaging radiation is present on both the top side and the bottom side of a substrate which is imaged by said apparatus.

31. An apparatus in accordance with Claim 20, wherein a rotatable mask is suspended over said substrate by a tensioning device which can be adjusted to control the amount of force applied to a surface in contact with said rotatable mask.