WO2016018880A1 - Apertureless cantilever-free tip arrays for scanning optical lithography and photochemical printing - Google Patents

Abstract

A tip array can include a tip substrate layer comprising a first surface and an oppositely disposed second surface, a plurality of tips fixed to the first surfaces, the tips comprising a tip end disposed opposite the first surface, a blocking layer coated on the first surface. The tip substrate layer is formed from a substrate material and the tips are formed from a tip material. The substrate material and the tip material each comprise an at least translucent material. The tips have a radius of curvature of less than about 1 μιη. The tips are substantially free from the blocking layer.

Description

APERTURELESS CANTILEVER-FREE TIP ARRAYS FOR SCANNING OPTICAL LITHOGRAPHY AND PHOTOCHEMICAL PRINTING

BACKGROUND

[0001] There are two categorically different approaches for defining patterns on surfaces, those based on the delivery of energy and those based on the delivery of materials. ^{[1 4]} The delivery of energy is the mainstay of the microelectronics community while the delivery of materials is commonly used in biological contexts where the materials of interest are chemically diverse and sensitive to harsh processing conditions. One recently developed set of techniques that spans this divide is cantilever-free scanning probe lithography (SPL) wherein materials or energy are deposited from an array of pens that rest on an elastomeric film on a rigid support. ^{[5 12]} This architecture affords the high resolution commonly observed in SPL in combination with high throughput by virtue of the simultaneous operation of as many as millions of pens. Given the widespread usage of energy delivery techniques, beam pen lithography (BPL), in which cantilever- free pens can be used as near- field probes to direct light onto surfaces in a massively parallel and multiplexed fashion, has aroused broad interest in low cost desktop nanofabrication and site- selective photochemistry.¹⁷' ^{13 14]} However, the need for rigid opaque materials and apertures at the tips of the pens in BPL constrains this technique from fully leveraging the advantages inherent to elastomeric pens with respect to molecular printing and necessitates a complicated nanofabrication step to open uniform sub-wavelength apertures at the tip of each probe.

SUMMARY

[0002] In accordance with an embodiment of the disclosure a tip array can include a tip substrate layer comprising a first surface and an oppositely disposed second surface, a plurality of tips fixed to the first surfaces, the tips comprising a tip end disposed opposite the first surface, a blocking layer coated on the first surface. The tip substrate layer is formed from a substrate material and the tips are formed from a tip material. The substrate material and the tip material each comprise an at least translucent material. The tips have a radius of curvature of less than about 1 μιη. The tips are substantially free from the blocking layer.

[0003] In accordance with another embodiment of the disclosure, a method for sub-micron scale patterning can include coating a tip array with a patterning composition, contacting a surface to be patterned with the tip array to deliver the patterning composition to the surface, and irradiating at least one tip of the tip array with a radiation source to transmit radiation through the tips and out the tip ends, thereby forming at least one indicia on the substrate. The patterning composition and/or the surface to be patterned can be reactive to the radiation.

[0004] In accordance with yet another embodiment, a method for sub-micron scale patterning can include contacting a photosensitive substrate with a tip array, irradiating at least one tip of the tip array with a radiation source, to transmit radiation through the tip and out the tip end; and exposing a portion of the photosensitive substrate with the transmitted radiation, thereby forming at least one indicia on the substrate.

[0005] In accordance with still another embodiment, a system for lithography can include a radiation source for emitting a radiation in a path, a tip array disposed in the radiation path such that the radiation, when active, is incident upon the tip substrate layer, and a substrate stage disposed for selective contacting of a substrate to the tip array.

[0006] In any of the foregoing embodiments of methods of patterning or systems for lithography the tip array can include a tip substrate layer having a first surface and an oppositely disposed second surface, a plurality of tips attached to the first surface, and a blocking layer coated on the first surface. The plurality of tips can be substantially free of the blocking layer.

[0007] In accordance with another embodiment of the disclosure, a method of making a tip array can include providing tip array that includes a tip substrate layer comprising a first surface and an oppositely disposed second surface, and a plurality of tips fixed to the first surface, the tips each comprising a tip end disposed opposite the first surface. The method can further include selectively coating a blocking layer on the first surface, wherein the tips remain substantially free of the blocking layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A is an optical image of a tip and a schematic illustration showing the four light paths present when elastomeric pyramidal tips are illuminated;

[0009] Figure IB is a schematic illustration of a method of making a tip array in accordance with an embodiment of the disclosure;

[0010] Figure 1C is a scanning electron microscopy image of a tip array in accordance with an embodiment of the disclosure;

[0011] Figure ID is a schematic illustration of scanning optical lithography using a tip array in accordance with an embodiment of the disclosure; [0012] Figure 2A is a dark field optical microscope image of a large region of developed photoresist patterns generated in accordance with an embodiment of the disclosure. Each 7x 3 array of dots is written by a single tip under the same exposure dose, but with a z-piezo extension that increases from left to right;

[0013] Figure 2B is a tapping-mode atomic force microscopy image of a typical dot array showing the change in size and shape with increasing z-piezo extension from left to right;

[0014] Figure 2C is graph showing the after size of features written at varying z-piezo extension by a method in accordance with an embodiment of the disclosure;

[0015] Figure 2D is a tapping-mode atomic force microscopy image of patterned dot arrays with varying exposure time from 1 second to 10 seconds and relative z-piezo extension of 0, 2, 4, and 6 μιη from bottom to top row, patterned in accordance with an embodiment of the disclosure;

[0016] Figure 2E is a graph of features size at initial contact as a function of exposure time;

[0017] Figure 3A is a schematic illustration of tilted lithography patterning using a tip array in accordance with an embodiment of the disclosure;

[0018] Figure 3B is scanning microscopy images of Au dot arrays generated at the left, middle, and right edges of an about 0.5 cm wide tip array in accordance with an embodiment of the disclosure. Average feature sizes were 2.91 + 0.12 μιη, 1.48 + 0.07 μιη, and 0.41 + 0.09 μιη from left to right. The scale bars are 5 μιη;

[0019] Figure 4A is a schematic illustration of photochemical printing of Rhodamine- modified thiol inks by thiol-ene photochemistry in accordance with an embodiment of the disclosure;

[0020] Figure 4B is a fluorescence microscope image ( _eX= 537-562 nm, λ_ετη= 570-640 nm) of 4 x 3 arrays patterned in accordance with an embodiment of the disclosure using illumination times of 1, 2, 3, and 4 min from bottom to top rows;

[0021] Figure 4C is a fluorescence microscope image of an array patterned by a single tip of a tip array in accordance with an embodiment of the disclosure, showing dots with (right 3 columns) and without (left column) UV illumination. The scale bar is 10 μιη;

[0022] Figure 4D is a graph showing the intensity profile of the patterned features of Figure 4C; [0023] Figure 5A is an image of intensity profiles generated by FDTD simulations at horizontal planes at the top, in the middle, and at the bottom of a photoresists and at a vertical plane with a tip size of 0.2 μιη. The scale bar is 2 μιη;

[0024] Figure 5B is an image of intensity profiles generated by FDTD simulations at horizontal planes at the top, in the middle, and at the bottom of a photoresists and at a vertical plane with a tip size of 1.2 μιη. The scale bar is 2 μιη;

[0025] Figure 5C is an image of intensity profiles generated by FDTD simulations at horizontal planes at the top, in the middle, and at the bottom of a photoresists and at a vertical plane with a tip size of 3.2 μιη. The scale bar is 2 μιη;

[0026] Figures 6A-6C is a scanning electron microscopy image of Au pattern arrays generated in accordance with an embodiment of the disclosure, illustrating change in feature size and shape obtained by adjusting the z-piezo extension and exposure time. The features in Figure 6B have an average feature size of 250 + 30 nm. The Au lines patterned in Figure 6C were obtained by adjusting the z-piezo extension to write pixels with different sizes.

DETAILED DESCRIPTION

[0027] Scanning optical lithography, such as beam pen lithography, can allow for patterning of sub-micron features over large areas with flexible pattern design, convenient, selective pen tip addressability, and low fabrication cost. As compared to conventional photolithography or contact printing in which only pre-formed patterns (i.e. photomasks) can be duplicated, scanning optical lithography can provide the flexibility to create different patterns by controlling the movement of a tip array 10 over the substrate and/or by selectively illuminating one or more of the pen tips 14 in the tip array 10. Thus, multiple "dots", for example, can be fabricated to achieve arbitrary features. This approach bypasses the need for, and costs associated with, photomask fabrication in conventional photolithography, allowing one to arbitrarily make many different types of structures without the hurdle of designing a new master via a throughput-impeded serial process. Conventional beam pen lithography tip arrays include a rigid and opaque coating on the surface of the tips with only the tip end being exposed through an aperture. Surprisingly, it is has been found that optical interaction with the surface is dominated by the light at the tip end of the tips when the opaque film from the tips is omitted and instead the tip arrays are provided with a blocking layer disposed on the substrate layer between adjacent pen tips. Elimination of the rigid opaque films from the tips, as is used with convention beam pen lithography tip arrays, beneficially allows for tuning of the illumination region from submicrometer to micrometer scale by reversibly deforming the tips. Additionally, the tip arrays in accordance with embodiments of the disclosure can be used to deliver both radiation and patterning compositions to a substrate, thereby allowing for photochemical patterning. In various embodiments, the tip arrays in accordance with embodiments of the disclosure can be used to deliver radiation and a patterning composition to a substrate in a single step, thereby allowing for control over surface reactions with combined approaches based on light, contact force, and material transfer.

[0028] The paths through which light can propagate through an elastomeric pyramid were analyzed. Referring to Figure 1A, in observing an elastomeric pyramid from the top, it was observed from the varying contrast in different regions that light incident on different areas is directed in different ways. Through ray tracing simulations of light normally incident on a tip array having pyramidal tips, it was observed that there are four distinct optical paths that may play a role in beam pen lithography: (a) light that is directed to the vicinity of the tip ends; (b) light that is incident on flat faces of the tips near the centers, (c) light that is incident on the flat faces of the tips near the edges, and (d) light that is incident on the flat substrate layer. Effective beam pen lithography generally requires that light path (a), light that is directed to the vicinity of the tip ends, dominates the delivery of optical energy to the surface. For this to occur, all other light paths must be marginalized. Light path (b), light that is incident on flat faces of the tips near the centers, internally reflects once in the tip and leaves via the opposing face at a 24° angle with respect to the surface to be patterned. This steep angle serves to diffuse this light broadly across the surface. Light path (c), light that is incident on the flat faces of the tips near the edges, accounts for about 40% of the light illuminating the tip. This light internally reflects twice in the tip and then leaves via the opposing face at a 2° angle, moving vertically away from the surface to be patterned. Light path (d), light that is incident on the flat substrate layer, is directly transmitted to the photosensitive surface, and represents an uncontrolled background illumination. It was beneficially found that blocking only light path (d) by providing a blocking layer on the substrate layer between adjacent tips, allowed for reliable scanning optical lithography.

[0029] The ray tracing simulations were performed using Persistence of Vision Raytracer Pty. Ltd. FDTD simulations were performed with a commercial package (Lumerical PFTD solutions v. 8.7.0). The refractive indices of photoresist and PDMS pyramidal tips were assumed to be 1.66 and 1.43, respectively. Finite-difference time domain (FDTD) was run with purely pyramidal structures. Due to the computation limitations, the pyramid size in the simulation was reduced to 8 μιη. Perfectly Matched Layers (PML) boundary condition was used in to absorb the electromagnetic fields at the simulation boundary. The Total Field Scattered Field (TFSF) plane wave source was used to avoid the light interaction with the simulation boundary. The light polarization was paralleled to the edge of the pyramidal tips. The spectral profile of the light source (LED ) was addressed by averaging the intensity profiles over the spectral range of the light source with the spectral line shape as the weighting factor.

[0030] Referring to Figures IB and ID, in accordance with embodiments of the disclosure, the tip array 10 includes a plurality of tips 14 attached to a tip substrate layer 12. The tip substrate layer 12 includes a first surface 13 and an oppositely disposed second surface 15. The tips 14 are attached to or extend from the first surface 13. The tips 14 and the tip substrate layer 12 are formed from a material which is at least translucent to the wavelength of radiation intended for use in patterning, e.g. in a range of 300 nm to 600 nm, and preferably the tips 14 are transparent to such light. A blocking layer 16 is provided on the first surface 13 of tip substrate layer 12 between adjacent tips 14. A majority of the surface of the tips is free of the blocking layer. In various embodiments, the tips are completely free of the blocking layer. Figure ID further illustrates illumination of the tips with radiation 18 passing through the tips, but being blocked by the blocking layer 16.

[0031] The tips 14 can be used to both channel the radiation to a surface in a massively parallel scanning probe lithographic process and to control one or more parameters such as the distance between the tip and the surface to be patterned, and the degree of tip

deformation. Control of such parameters can allow one to take advantage of near-field effects. In one embodiment, the tips 14 are elastomeric and reversibly deformable, which can allow the tip array 10 to be brought in contact with the surface to be patterned without damage to the surface to be patterned or the tip array 10. This contact can ensure the generation of near-field effects and can allow for tuning of the illumination region.

Tip Array

[0032] Referring to Figures IB and ID, an embodiment of a tip array 10 in accordance with the disclosure includes a tip substrate layer 12 and a plurality of tips 14 fixed to the tip substrate layer 12. The tip substrate layer 12 has a first surface 13 to which the plurality of tips 14 are attached and an oppositely disposed second surfacel5. The tip substrate layer 12 and the plurality of tips 14 are formed of a transparent polymer. The tip substrate layer 12 and the tips 14 can be formed of the same polymer or can be formed of different materials. When the tip substrate layer 12 and the tips 14 are formed of different materials, the tip material does not extend into the tip substrate layer 12. That is, the tip material extends only from the first surface of the tip substrate layer to the tip end 20. The tip substrate layer 12 is a single continuous material.

[0033] The tip array 10 further includes a blocking layer 16 coated on the first surface 13 of the tip substrate layer 12 between adjacent tips 14. The tips 14 are substantially free of the blocking layer 16.

[0034] The tip substrate layer 12 can have any suitable thickness, for example in a range of about 5 μιη to about 5 mm, about 50 μιη to about 100 μιη, or about 1 mm to about 5 mm. For example, the tip substrate layer 12 can have a minimum thickness of about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, or 5000 μπι. For example, the tip substrate layer 12 can have a maximum thickness of about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, or 5000 μιη. The thickness of the tip substrate layer 12 can be decreased as the rigidity of the polymer used to form the tip substrate layer 12 increases. For example, for a gel polymer (e.g., agarose), the tip substrate layer 12 can have a thickness in a range of about 1 mm to about 5mm. For other, more rigid, polymers (e.g., PDMS) the tip substrate layer can have a thickness in a range of about 50 μιη to about 100 μιη, for example. The combined thickness of the tip substrate layer 12 and the tips 14 can be in range of about 5 μιη to about 5 mm, or about 5 μιη to 1 mm. For example, the combined thickness can be less than 1 mm or less than 0.5 mm, or less than 0.3 mm, or less than 0.2 mm, or less than 0.1 mm, or less than 50 μιη, or less than 25 μιη. For example, for a gel polymer (e.g., agarose), the combined thickness can be up to about 5 mm. For example, for other polymers (e.g., PDMS) the combined thickness can be less than about 200 μιη, preferably less than about 150 μιη, or more preferably about 100 μιη.

[0035] The tip substrate layer 12 can be attached to a transparent rigid support, for example, formed from glass, silicon, quartz, ceramic, polymer, or any combination thereof. The rigid support is preferably highly rigid and has a highly planar surface upon which to mount the tip array 10. [0036] The tip arrays are non-cantilevered and comprise tips 14 which can be designed to have any shape or spacing (pitch) between them, as needed. The shape of each tip can be the same or different from other tips 14 of the array, and preferably the tips 14 have a common shape. Contemplated tip shapes include spheroid, hemispheroid, toroid, polyhedron, cone, cylinder, and pyramid (trigonal or square). The tips 14 have a base portion fixed to the tip substrate layer 12. The base portion preferably is larger than the tip end portion. The base portion can have an edge length in a range of about 1 μιη to about 50 μιη, or about 5 μιη to about 50 μιη . For example, the minimum edge length can be about 1, 2, 3, 4, 5, 6, 7, 8, 9,

10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50 μιη. For example, the maximum edge length can be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,

11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50 μιη.

[0037] In accordance with an embodiment of the disclosure, a tip array 10 can contain thousands of tips 14, preferably having a pyramidal shape. The substrate-contacting (tip end) portions of the tips 14 each can have a diameter in a range of about 10 nm to about 1 μιη. For example, the minimum diameter can be about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nm. For example, the minimum diameter can be about 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nm. The substrate-contacting portions of the tips 14 are preferably sharp, so that each is suitable for forming submicron patterns, e.g., less than about 500 nm. The sharpness of the tip is measured by its radius of curvature. The tips 14 can have a radius of curvature, for example, of below about 1 μιη, and can be less than about 0.9 μιη, less than about 0.8 μιη, less than about 0.7 μιη, less than about 0.6 μιη, less than about 0.5 μιη, less than about 0.4 μιη, less than about 0.3 μιη, less than about 0.2 μιη, less than about 0.1 μιη, less than about 90 nm, less than about 80 nm, less than about 70 nm, less than about 60 nm, or less than about 50 nm.

[0038] The tip-to-tip spacing between adjacent tips 14 (tip pitch) can be in a range of about 1 μιη to about over 10 mm, or about 20 μιη to about 1 mm. For example, the minimum tip- to-tip spacing can be about 1 μιη, 2 μιη, 3 μιη, 4 μιη, 5 μιη, 6 μιη, 7 μιη, 8 μιη, 9 μιη, 10 μιη, 15 μιη, 20 μιη, 25 μιη, 30 μιη, 35 μιη, 40 μιη, 45 μιη, 50 μιη, 55 μιη, 60 μιη, 65 μιη, 70 μιη, 75 μιη, 80 μιη, 85 μιη, 90 μιη, 95 μιη, 100 μιη, 200 μιη, 300μιη, 400μιη , 500μιη , 600 μιη , 700 μιη, 800 μιη, 900 μιη, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm. For example, the maximum tip-to-tip spacing can be about 1 μιη, 2 μιη, 3 μιη, 4 μιη, 5 μιη, 6 μιη, 7 μιη, 8 μm, 9 μιη, 10 μm, 15 μιη, 20 μm, 25 μm, 30 μιη, 35 μm, 40 μιη, 45 μm, 50 μm, 55 μιη, 60 μm, 65 μιη, 70 μm, 75 μm, 80 μιη, 85 μm, 90 μιη, 95 μm, 100 μm, 200 μιη, 300μm, 400μm , 500μιη , 600 μm , 700 μιη, 800 μm, 900 μιη, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm.

[0039] The tips 14 of the tip array 10 can be designed to have any desired thickness, but typically the thickness of the tip array 10 is about 50 nm to about 50 μιη, about 50 nm to about 1 μιη, about 10 μιη to about 50 μιη, about 50 nm to about 500 nm, about 50 nm to about 400 nm, about 50 nm to about 300 nm, about 50 nm to about 200 nm, or about 50 nm to about 100 nm. For example, the minimum thickness can be about 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μιη, 5 μιη, 10 μιη, 15 μιη, 20 μιη, 25 μιη, 30 μιη, 35 μιη, 40 μιη, 45 μιη, or 50 μιη. For example, the maximum thickness can be about 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μπι, 5 μπι, 10 μπι, 15 μιη, 20 μιη, 25 μιη, 30 μιη, 35 μιη, 40 μιη, 45 μιη, or 50 μιη. The thickness of the tip array 10 can be decreased as the rigidity of the polymer used to form the tip substrate layer increases. For example, for a gel polymer (e.g., agarose), the tip array 10 can have a thickness in a range of about 10 μιη to about 50 μιη. For other polymers (e.g., PDMS), for example, the tip array 10 can have a thickness of about 50 nm to about 1 μιη. As used herein, the thickness of the tip array 10 refers to the distance from the tip end to the base end of a tip. The tips 14 can be arranged randomly or in a regular periodic pattern (e.g., in columns and rows, in a circular pattern, or the like).

[0040] Polymeric materials suitable for use in the tip array 10 can have linear or branched backbones, and can be crosslinked or non-crosslinked, depending upon the particular polymer and the degree of compressibility desired for the tip. Cross-linkers refer to multi-functional monomers capable of forming two or more covalent bonds between polymer molecules. Non-limiting examples of cross-linkers include such as trimethylolpropane trimethacrylate (TMPTMA), divinylbenzene, di-epoxies, tri-epoxies, tetra-epoxies, di-vinyl ethers, tri-vinyl ethers, tetra-vinyl ethers, and combinations thereof.

[0041] Thermoplastic or thermosetting polymers can be used, as can crosslinked elastomers. In general, the polymers can be porous and/or amorphous. A variety of elastomeric polymeric materials is contemplated, including polymers of the general classes of silicone polymers and epoxy polymers. Polymers having low glass transition temperatures such as, for example, below 25°C or more preferably below -50°C, can be used. Diglycidyl ethers of bisphenol A can be used, in addition to compounds based on aromatic amine, triazine, and cycloaliphatic backbones. Another example includes Novolac polymers. Other contemplated elastomeric polymers include methylchlorosilanes, ethylchlorosilanes, and phenylchlorosilanes, polydimethylsiloxane (PDMS). Other materials include polyethylene, polystyrene, polybutadiene, polyurethane, polyisoprene, polyacrylic rubber, fluoro silicone rubber, and fluoroelastomers.

[0042] Further examples of suitable polymers that may be used to form a tip can be found in U.S. Patent No. 5,776,748; U.S. Patent No. 6,596,346; and U.S. Patent No. 6,500,549, each of which is hereby incorporated by reference in its entirety. Other suitable polymers include those disclosed by He et al., Langmuir 2003, 19, 6982-6986; Donzel et al., Adv. Mater. 2001, 13, 1164-1167; and Martin et al., Langmuir, 1998, 14-15, 3791-3795, which are also incorporated herein by reference in their entireties. Hydrophobic polymers such as polydimethylsiloxane can be modified either chemically or physically by, for example, exposure to a solution of a strong oxidizer or to an oxygen plasma.

[0043] The polymer of the tip array 10 can be a polymer gel. The gel polymer can comprise any suitable gel, including hydrogels and organogels. For example, the polymer gel can be a silicon hydrogel, a branched polysaccharide gel, an unbranched polysaccharide gel, a polyacrylamide gel, a polyethylene oxide gel, a cross-linked polyethylene oxide gel, a poly(2- acrylamido-2-methyl-l-propanesulfonic acid) (polyAMPS) gel, a polyvinylpyrrolidone gel, a cross-linked polyvinylpyrrolidone gel, a methylcellulose gel, a hyaluronan gel, and combinations thereof. For example, the polymer gel can be an agarose gel. By weight, gels are mostly liquid, for example the gel can be greater than 95% liquid, yet behave like a solid due to the presence of a cross-linked network within the liquid.

[0044] The material used to form the tip array 10 has a suitable compression modulus and surface hardness to prevent collapse of the tip during contact with the surface, but too high a modulus and too great a surface hardness can lead to a brittle material that cannot adapt and conform to a substrate surface during exposure. As disclosed in Schmid, et al.,

Macromolecules, 33:3042 (2000), vinyl and hydrosilane prepolymers can be tailored to provide polymers of different modulus and surface hardness. Thus, in another type of embodiment, the polymer can be a mixture of vinyl and hydrosilane prepolymers, wherein the weight ratio of vinyl prepolymer to hydrosilane crosslinker is about 5: 1 to about 20: 1, about 7: 1 to about 15: 1, or about 8: 1 to about 12: 1. [0045] The material used to form the tip array 10 preferably will have a surface hardness of about 0.2% to about 3.5% of glass, as measured by resistance of a surface to penetration by a hard sphere with a diameter of 1 mm, compared to the resistance of a glass surface (as described in Schmid, et al., Macromolecules, 33:3042 (2000) at p 3044). The surface hardness optionally can be about 0.3% to about 3.3%, about 0.4% to about 3.2%, about 0.5% to about 3.0%, or about 0.7% to about 2.7% of glass. The polymers of the tip array 10 can have a compression modulus of about 1 MPa to about 300 MPa, about 10 MPa to about 300 MPa, about 50 MPa to about 200 MPa, about 100 MPa to about 300 MPa, or about 1 MPa to about 50 MPa. The tip array 10 preferably comprises a compressible polymer which is Hookean under pressures of about 1 MPa to about 300 MPa or about 10 MPa to about 300 MPa. The linear relationship between pressure exerted on the tip array 10 and the feature size allows for control of the near field and feature size using the disclosed methods and tip arrays.

[0046] The blocking layer 16 disposed on the first surface 13 of the tip substrate layer 12 serves as a radiation blocking layer, preventing a surface to be patterned from being exposed to radiation passing through the tip substrate layer between the tips (optical path (d) described above). The blocking layer 16 can be formed of any material suitable for blocking (e.g., reflecting) a type of radiation used in the lithography process. For example, the blocking layer 16 can be a metal, such as gold, when used with UV light. Other suitable blocking layers include, but are not limited to, gold, chromium, titanium, silver, copper, nickel, silicon, aluminum, opaque organic molecules and polymers, and combinations thereof. In one embodiment, the blocking layer can includes a layer of gold and a layer of titanium. The blocking layer 16 can have any suitable thickness, for example in a range of about 40 nm to about 5000 nm. For example, the minimum thickness can be about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000 nm. For example, the maximum thickness can be about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000 nm.

Tip Array Formation

[0047] The reversibly deformable tip arrays can be formed in accordance with methods known in the art. For example, U.S. Patent Application Publication No. 2011/013220 discloses methods of making polymeric tip arrays. For example, the tip portion of the tip arrays can be made with a master prepared by conventional photolithography and subsequent wet chemical etching. The mold can be engineered to contain as many tips 14 arrayed in any fashion desired. The tips 14 of the tip array 10 can be any number desired, and contemplated numbers of tips 14 include about 1000 tips 14 to about 15 million tips, or greater. The number of tips 14 of the tip array 10 can be greater than about 1 million, greater than about 2 million, greater than about 3 million, greater than about 4 million, greater than 5 million tips 14, greater than 6 million, greater than 7 million, greater than 8 million, greater than 9 million, greater than 10 million, greater than 11 million, greater than 12 million, greater than 13 million, greater than 14 million, or greater than 15 million tips.

[0048] Optionally, the tips 14 can be cleaned, for example, using oxygen plasma, prior to coating with the blocking layer 16. Referring to Figure IB, in one embodiment, the tip array 10 including the first surface 13 of the tip substrate layer 12 and the tips 14 can be coated with the material forming the blocking layer 16. The tip array can be coated using any known methods including, but not limited to, spin coating, dip coating, brush coating, and evaporative coating. A protective layer 22, for example, and etch stop layer, can be coated onto the blocking layer portion disposed on the first surface of the tip array. The exposed portion of the blocking layer (i.e., the portion disposed on the tips) can then be removed, for example, by etching. Chemical or mechanical etching can be used. Ion etching (reactive or ablation) can also be used. A suitable protective layer, for example, is poly (methyl methacrylate) (PMMA). Photoresists can also be used as the protective layer. For example, Shipley Microposit SI 800 Series photoresists or AZ 4000 series photoresists can be used.

[0049] In other embodiments, the blocking layer material can be selectively coated on the first surface of the tip substrate layer. For example, the tips can be masked prior to coating the blocking layer and then the blocking layer can be applied and removed from the tips with removal of the mask. In yet another embodiment, the blocking layer can be selectively applied to a rigid support, such as a glass support, before the tip array is attached to the rigid support. The blocking layer is selectively applied to the rigid support such that it is disposed between adjacent tips when the tip array is attached to the rigid support.

Surfaces to be Patterned

[0050] The surfaces to pattern by the tip arrays in accordance with the disclosure can include any suitable substrate. Substrates suitable for use in methods disclosed herein include, but are not limited to, metals, alloys, composites, crystalline materials, amorphous materials, conductors, semiconductors, optics, fibers, inorganic materials, glasses, ceramics (e.g., metal oxides, metal nitrides, metal silicides, and combinations thereof), zeolites, polymers, plastics, organic materials, minerals, biomaterials, living tissue, bone, films thereof, thin films thereof, laminates thereof, foils thereof, composites thereof, and combinations thereof. A substrate can comprise a semiconductor such as, but not limited to: crystalline silicon, polycrystalline silicon, amorphous silicon, p-doped silicon, n-doped silicon, silicon oxide, silicon

germanium, germanium, gallium arsenide, gallium arsenide phosphide, indium tin oxide, and combinations thereof. A substrate can comprise a glass such as, but not limited to, undoped silica glass (Si0₂), fluorinated silica glass, borosilicate glass, borophosphorosilicate glass, organosilicate glass, porous organosilicate glass, and combinations thereof. The substrate can be a non-planar substrate, such as pyrolytic carbon, reinforced carbon-carbon composite, a carbon phenolic resin, and the like, and combinations thereof. A substrate can comprise a ceramic such as, but not limited to, silicon carbide, hydrogenated silicon carbide, silicon nitride, silicon carbonitride, silicon oxynitride, silicon oxycarbide, high-temperature reusable surface insulation, fibrous refractory composite insulation tiles, toughened unipiece fibrous insulation, low-temperature reusable surface insulation, advanced reusable surface insulation, and combinations thereof. A substrate can comprise a flexible material, such as, but not limited to: a plastic, a metal, a composite thereof, a laminate thereof, a thin film thereof, a foil thereof, and combinations thereof.

[0051] In various embodiment, the surface to be patterned is capable of interacting or reacting with a patterning composition upon exposure to radiation. Suitable surfaces include, but are not limited to, alkene-functionalized surfaces, thiol-functionalized surfaces, carboxyl- functionalized surfaces, hydroxyl-functionalized surfaces, and combinations thereof.

[0052] For example, in various embodiments, the surface to be patterned is one which can be advantageously affected by exposure to radiation. For example, the substrate can be photosensitive or can include a photosensitive layer 20. For example, the photosensitive substrate or photosensitive layer 20 can be a resist layer. The resist layer can be any known resist material, for example SHIPLEY 1805 (MicroChem Inc.). Other suitable resist materials include, but are not limited to, Shipleyl813 (MicroChem Inc.), Shipleyl830 (MicroChem Inc.), PHOTORESIST AZ1518 (MicroChemicals, Germany), PHOTORESIST AZ5214 (MicroChemicals, Germany), SU-8, and combinations thereof. Other examples of photosensitive materials include, but are not limited to, liquid crystals and metals. For examples, the substrate can include metal salts that can be reduced when exposed to the radiation. Substrates suitable for use in methods disclosed herein include, but are not limited to, metals, alloys, composites, crystalline materials, amorphous materials, conductors, semiconductors, optics, fibers, inorganic materials, glasses, ceramics (e.g., metal oxides, metal nitrides, metal silicides, and combinations thereof), zeolites, polymers, plastics, organic materials, minerals, biomaterials, living tissue, bone, and laminates and combinations thereof. The substrate can be in the form of films, thin films, foils, and combinations thereof. A substrate can comprise a semiconductor including, but not limited to one or more of:

crystalline silicon, polycrystalline silicon, amorphous silicon, p-doped silicon, n-doped silicon, silicon oxide, silicon germanium, germanium, gallium arsenide, gallium arsenide phosphide, indium tin oxide, graphene, and combinations thereof. A substrate can comprise a glass including, but not limited to, one or more of undoped silica glass (Si0₂), fluorinated silica glass, borosilicate glass, borophosphorosilicate glass, organosilicate glass, porous organosilicate glass, and combinations thereof. The substrate can be a non-planar substrate, including, but not limited to, one or more of pyrolytic carbon, reinforced carbon-carbon composite, a carbon phenolic resin, and combinations thereof. A substrate can comprise a ceramic including, but not limited to, one or more of silicon carbide, hydrogenated silicon carbide, silicon nitride, silicon carbonitride, silicon oxynitride, silicon oxycarbide, high- temperature reusable surface insulation, fibrous refractory composite insulation tiles, toughened unipiece fibrous insulation, low-temperature reusable surface insulation, advanced reusable surface insulation, and combinations thereof. A substrate can comprise a flexible material, including, but not limited to one or more of: a plastic, a metal, a composite thereof, a laminate thereof, a thin film thereof, a foil thereof, and combinations thereof.

[0053] The photosensitive substrate or the photosensitive layer 20 can have any suitable thickness, for example in a range of about 20 nm to about 5000 nm. For example, the minimum photosensitive substrate or photosensitive layer 20 thickness can be about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450 or 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000 nm. For example, the maximum photosensitive substrate or photosensitive layer 20 thickness can be about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450 or 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000 nm. The diameter of the indicia formed by the tip array 10 can be modulated by modifying the resist material used and/or the thickness of the photosensitive substrate or photosensitive layer 20. For example, under the same radiation conditions, a thicker photosensitive layer can result in indicia having larger diameters. At constant photosensitive layer thickness, an increase radiation intensity can results in indicia having larger diameters.

Patterning

[0054] Patterning can be performed using any suitable platform, for example, a Park AFM platform (XEP, Park Systems Co., Suwon, Korea) equipped with a halogen light source. As another example, a Zeiss microscope can be used with a light source having a wavelength in a range of about 360 nm to about 450 nm. Movement of the tip array 10 when using the Zeiss microscope can be controlled, for example, by the microscope stage.

[0055] In accordance with an embodiment of the disclosure, a method of patterning can include bringing a tip array 10 into contact with a surface having a photosensitive layer 20, followed by exposure (e.g. illumination) of the top surface (the substrate layer) of the tip array 10 with a radiation source. As a result of the blocking layer 16 blocking the radiation (e.g., by reflection) from transmitting through the tip substrate layer (optical path d), the radiation is transmitted through the tip, primarily through optical path (a). Historically, photolithography has used ultraviolet light from gas-discharge lamps using mercury, sometimes in combination with noble gases such as xenon. These lamps produce light across a broad spectrum with several strong peaks in the ultraviolet range. This spectrum is filtered to select a single spectral line, for example the "g-line" (436 nm) or "i-line" (365 nm). More recently, lithography has moved to "deep ultraviolet," for example wavelengths below 300 nm, which can be produced by excimer lasers. Krypton fluoride produces a 248-nm spectral line, and argon fluoride a 193-nm line. In principle, the type of radiation used with the present apparatus and methods is not limited. One practical consideration is compatibility with the pen array materials. Radiation in the wavelength range of about 300 nm to about 600 nm is preferred, optionally 380 nm to 420 nm, for example about 365 nm, about 400 nm, or about 436 nm. Other suitable wavelengths include about 100 nm to about 900 nm, about 150 nm to about 300 nm, about 500 nm to about 900 nm. For example, the radiation optionally can have a minimum wavelength of about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, or 900 nm. For example, the radiation optionally can have a maximum wavelength of about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, or 900 nm.

[0056] The photosensitive layer can be exposed by the radiation transmitted through the polymer tip for any suitable time, for example in a range of about 1 second to about 1 minute. For example, the minimum exposure time can be about 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 20, 30, 40, 50, or 60 seconds. For example, the maximum exposure time can be about 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 20, 30, 40, 50, or 60 seconds.

[0057] The method can further include developing the photosensitive layer 20, for example by any suitable process known in the art. For example, when a resist layer is used, the exposed resist layer can be developed for by exposed for about 30 seconds in MF319 (Rohm & Haas Electronic Materials LLC). The resist layer can be a positive resist or a negative resist. If a positive resist layer is used, developing of the resist layer 20 removes the exposed portion of the resist layer. If a negative resist layer is used, developing of the resist layer removes the unexposed portion of the resist layer. Optionally, the method can further include depositing a patterning layer on the substrate surface after exposure followed by lift off of the resist layer to thereby form the patterning layer into the indicia printed on the resist layer by BPL. The patterning layer can be a metal, for example, and can be deposited, for example, by thermal evaporation. The resist lift off can be performed using, for example, acetone.

[0058] Propagation of light through a tip array in accordance with embodiments of the disclosure was tested by illuminating a photoresist surface. The tip array was mounted on a scanning probe system (XE150, Park System) and leveled with respect to the substrate to be patterned. The substrate was pre-coated with a positive-tone photoresist. Other suitable substrates for patterning are described in detail below. The tip array was brought into contact with the surface and illuminated from the back side for a specified time, using a radiation source having a wavelength of 405 nm. As described herein, other suitable wavelengths can be used depending on the substrate to be patterned or photochemical process being induced. The light was guided to individual tips using a digital micromirror device, which allowed for independent control of the location of the tip array, contact pressure, and illumination time. After the exposure, the surface was treated with a developer that caused the portion of the photoresist that had been exposed to dissolve, leaving a physical remnant of the light intensity profile. As shown in Figure 2A, a 7 x3 dot array was exposed to 4 seconds of light with a relative z-piezo extension (Z_ext) that gradually increased for 0 μιη to 6 μιη in each row. After developing the photoresist, a large region of uniform duplicates of this dot array pattern was observed, which confirmed that each tip in the 20,000 tip array generated a copy of the pattern.

[0059] Referring to Figure 2B, the nanoscale morphologies of the patterned features were characterized by atomic force microscopy. The size and shape of the exposed region did not change significantly as Z_ext was increase from 0 μιη to 1 μιη. The developed regions corresponded to roughly circular holes having a full width at half maximum of about 400 nm and a maximum depth of about 200 nm. This confirmed that the optical interaction between the tip array of the disclosure and the surface to be patterned is dominated by light near the apex (optical path (a) described above) and that light exiting through the faces (optical paths (b) and (c)) did not contribute significantly to the light intensity on the surface to be patterned.

[0060] Varying the exposure time can be used to vary the size of the patterned feature. For example, referring to Figures 2D and 2E, by varying the exposure time, sub-wavelength features down to 250 nm (about 0.6λ) were obtained. Referring to Figure 5, these results are in agreement with finite-difference time-domain (FDTD) calculations of light propagation at the tip end of a PDMS pyramidal tip. In particular, the FDTD calculation suggests that the light at the tip end is about seven times more intense than the incident light.

[0061] The tips of the tip arrays in accordance with embodiments of the disclosure can advantageously be reversibly deformed to tailor the amount of optical energy delivered to the surface. This can allow for force-dependent patterning with a z-piezo extension sweep. It was observed that by increasing the Z_ext from 1 μιη to 6 μιη, exposed features changes from round dots to square features having four protruding corners. The applied pressure on the tip array and corresponding deformation of the tips can be used to tailor the region of the substrate that is exposed to light and provide a reversible change in patterned feature size. Referring to Figure 2D, it was observed that by increasing the exposure time, the centers of these larger features can be filled with minimal loss of optical confinement. Thus, the larger, square features can still be reliable used for lithography.

[0062] In accordance with another embodiment of the disclosure, a method for patterning a feature on a surface can include patterning a compound on a surface and delivering radiation during patterning to induce a reaction in the compound and/or between the compound and the surface. Radiation can be delivered through the tip array in accordance with the method described above. The radiation can be delivered substantially simultaneously with the delivery of the patterning composition to the surface. Alternatively, the tip array can be illuminated after the tip array is contacted with the surface to deliver the patterning composition to the surface. In yet another embodiment, the tip array can be illuminated prior to contacting the surface to deliver the patterning composition to the surface.

[0063] Advantageously, because a blocking layer is not provided on the tips themselves, the tip arrays in accordance with embodiments of the disclosure can combine molecular printing of an ink and delivery of optical energy. Like polymer pen arrays, the tips can be coated in an ink and the substrate can be contacted with the tips to deliver the ink to the substrate. The tip arrays in accordance with the disclosure can also deliver radiation, such as optical energy, during patterning. Thus, in accordance with embodiments of the disclosure, the tip arrays can be used to print molecules and drive chemical reactions with radiation, such as light. For example, the radiation can be delivered substantially simultaneously with the delivery of the ink to cause a reaction in the ink and/or between the ink and the surface to be patterned. Referring to Figure 4A, the tip arrays in accordance with embodiments of the disclosure were used to pattern a thiol molecule modified with fluorescent Rhodamine B dye onto an alkene-functionalized surface using thiol-ene photo "click" chemistry. Prior to patterning, the tips were spin coated with a mixture of the fluorescent thiol, 2,2-dimethoxy-2- phenylacetophenone (DMPA) as a photoinitiator and glycerol as a high viscosity liquid matrix. The inked tip array was brought into contact with an alkene-terminated silicon substrate to write a 4 x 3 dot array while the tips array was illuminated by UV light (365 nm, 150-200 mW/cm ) to induce local surface photo-click reactions.

[0064] The effect of the illumination was analyzed by varying the dwell time between 1 min and 4 min, as well as a control in which a column of 4 dots was patterned with the same dwell times but no illumination. Referring to Figure 4B, after patterning and sonication of the patterned surface in ethanol for 30 minutes, the samples were characterized using fluorescence microscopy ke_X = 537-562 nm, e_m = 570-640 nm). Referring to Figures 4C and 4D, it was found that the fluorescence intensity gradually increased with dwell time, while the control dots showed very little fluorescence and did not change intensity with dwell time. In contrast to polymer pen lithography, spurious dots form incidental contact during leveling or a diffusion-controlled feature size was not observed. Without intending to be bound by theory, it is believed that these were not observed due to the efficient light confinement at the tip. Additionally, while the optical intensity profile is not isotropic at high deformation, all features observed were round. Without intending to be bound by theory, it is believed that the feature shape is defined by molecular printing in addition to confinement of the light. It is further believed that the combined molecular printing-illumination based approach can be used to define features that would be smaller than either technique alone.

[0065] Any suitable patterning compositions and substrates can be used. For example, the patterning composition can include water soluble polymers, such as Poly(ethylene glycol) or poly(ethylene oxide)-b-poly(2-vinylpyridine); nonvolatile liquids, such as glycerol or undecane and polymers that are soluble in them such as polystyrene -b- poly(2-vinylpyridine); small molecules such as a 16-mercaptohexadecanoic acid or octadecanethiol, and

combinations thereof. For example, the patterning composition can be illuminated with the tip array to induce a chemical reaction such as thiol-ene photo "click" chemistry, thiol- acrylate photopolymerization, styrene photopolymerization, and combinations thereof.

[0066] In any of the patterning methods described herein, the tip array 10 and/or the surface to be patterned can be moved during patterning to form the desired indicia. For example, in one embodiment, the tip array 10 is moved while the substrate is held stationary. In another embodiment, the tip array 10 is held stationary while the substrate is moved. In yet another embodiment, both the tip array 10 and the substrate are moved. For example, large arrays of dots can be made simultaneously by moving the array of the surface with a piezo stage while illuminating the tip array 10 from the back side of the tips 14, for example, through the tip substrate layer 12.

[0067] In any of the patterning methods described herein, the individual tips 14 within a tip array can be addressed by selective illumination. For example, patterning can be achieved with the illumination of fewer than all of the tips 14 in the array, for example with one or a selected plurality of the tips 14 in the tip array 10. Selective illumination of the tips 14 can be performed, for example, by selectively focusing light through the microscopic bases of each tip. The tip array 10 can also include one or more spatial light modulators capable of blocking certain tips 14 from exposure to the light. The spatial light modulators can be static and/or dynamically controllable. For example, the spatial light modulates can be shutters. The spatial light modulators can be formed using a variety of materials, including, for example, liquid crystals. The spatial light modulators can be, for example, a mask, which is not dynamically controllable. The spatial light modulators can be placed or formed as a part of the tip substrate layer 12. Because the base of the tips 14 has edge lengths on the order of microns, the spatial light modulators need not be created on the nanoscale in order to result in sub-micron sized indicia. Rather it is the channeling of the radiation through the transparent polymer and the aperture 18 that allows for the sub-micron patterning. Tip addressability has been a major challenge for SPL methods. With passive arrays, one simply achieves duplication - each tip does exactly what the other tips 14 do. Many different methods of actuation have been evaluated with limited success, especially where lithography is the primary goal. Thermal, mechanical, electrical and magnetic actuation have all been studied. With the tip array in accordance with the disclosure, the radiation can be used as a convenient method to achieve multiplexed addressability of each tip within a complex and large array.

[0068] For example, a photo mask, for example, a Cr photo mask, can be used to cover all of the bases of the tips (e.g. on the second surface of the tip substrate layer) that one wants to turn off in an experiment. This approach allows for two orthogonal levels of control, using selective illumination for tip-attenuation and tip movement. When coupled with spatial light modulator, each tip can be individually addressed to fabricate different patterns. For example, a portion of the tips 14 in a tip array 10 can be selectively illuminated and first pattern can be formed. The tip array 10 can then be shifted and a second pattern can be formed. The tip array 10 can be shifted, for example, a distance at least equal to the tip pitch to form with the second pattern step a variety of different patterns on the substrate. For example, as a result of the selective illumination of the tips 14, regions of the substrate would include only the first pattern, only the second pattern, or a combination of both patterns.

[0069] In any of the embodiments of the methods of patterning, the features that can be patterned range from sub- 100 nm to 1 mm in size or greater. As discussed above, the feature size and/or feature shape can be controlled by altering the exposure time and/or the contacting pressure of the tip array 10.

[0070] The tip arrays can exhibit pressure dependence which results from the compressible nature of the polymer used to form the tip array 10. Indeed, the microscopic, preferably pyramidal, tips 14 can be made to deform with successively increasing amounts of applied pressure, which can be controlled by simply extending the piezo in the vertical direction (z- piezo). The controlled deformation of the tip array 10 can be used as an adjustable variable, allowing one to control tip-substrate contact area and resulting feature size. The pressure of the contact can be controlled by the z-piezo of a piezo scanner. The more pressure (or force) exerted on the tip array 10, the larger the feature size. Thus, any combination of contacting time and contacting force/pressure can provide a means for the formation of a feature size from about 30 nm to about 1 mm or greater. The contacting pressure of the tip array 10 can be about 10 MPa to about 300 MPa.

[0071] At very low contact pressures, such as pressures of about 0.01 to about 0.1 g/cm² for the preferred materials described herein, the feature size of the resulting indicia is independent of the contacting pressure, which allows for one to level the tip array 10 on the substrate surface without changing the feature size of the indicia. Such low pressures are achievable by 0.5 μιη or less extensions of the z-piezo of a piezo scanner to which a tip array 10 is mounted, and pressures of about 0.01 g/cm 2 to about 0.1 g/cm 2 can be applied by z- piezo extensions of less than 0.5 μιη. This "buffering" pressure range allows one to manipulate the tip array 10, substrate, or both to make initial contact between tips 14 and substrate surface without compressing the tips 14, and then using the degree of compression of tips 14 (observed by changes in reflection of light off the inside surfaces of the tips 14) to achieve a uniform degree of contact between tips 14 and substrate surface. This leveling ability is important, as non-uniform contact of the tips 14 of the tip array 10 can lead to nonuniform indicia. Given the large number of tips 14 of the tip array 10 (e.g., 11 million in an example provided herein) and their small size, as a practical matter it may be difficult or impossible to know definitively if all of the tips 14 are in contact with the surface. For example, a defect in a tip or the substrate surface, or an irregularity in a substrate surface, may result in a single tip not making contact while all other tips 14 are in uniform contact. Thus, the disclosed methods provide for at least substantially all of the tips 14 to be in contact with the substrate surface (e.g., to the extent detectable). For example, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the tips 14 will be in contact with the substrate surface.

[0072] The leveling of the tip array 10 and substrate surface with respect to one another can be assisted by the transparent, or at least translucent nature of the tip array 10 and tip substrate layer 12, which allow for detection of a change in reflection of light that is directed from the top of the tip array 10 (i.e., behind the base of the tips 14 and common substrate) through to the substrate surface. The intensity of light reflected from the tips 14 of the tip array 10 increases upon contact with the substrate surface (e.g., the internal surfaces of the tip array 10 reflect light differently upon contact). By observing the change in reflection of light at each tip, the tip array 10 and/or the substrate surface can be adjusted to effect contact of substantially all or all of the tips 14 of the tip array 10 to the substrate surface. Thus, the tip array 10 and common substrate preferably are translucent or transparent to allow for observing the change in light reflection of the tips 14 upon contact with the substrate surface. Likewise, any rigid backing material to which the tip array 10 is mounted is also preferably at least transparent or translucent. The tip arrays can also be leveled using force feedback leveling as described in U.S. Patent No. 8,745,761, the disclosure of which is incorporated herein by reference in its entirety.

[0073] In any of the patterning methods disclosed herein, the contacting time for the tips 14 can be from about 0.001 seconds to about 60 seconds. For example, the minimum contact time can be about 0.001, 0.01, 0.1, 1, 10, 20, 30, 40, 50, or 60 seconds. For example, the maximum contact time can be about 0.001, 0.01, 0.1, 1, 10, 20, 30, 40, 50, or 60 seconds. The contacting force can be controlled by altering the z-piezo of the piezo scanner or by other means that allow for controlled application of force across the tip array 10.

[0074] The substrate surface can be contacted with a tip array 10 a plurality of times, wherein the tip array 10, the substrate surface or both move to allow for different portions of the substrate surface to be contacted. The time and pressure of each contacting step can be the same or different, depending upon the desired pattern. The shape of the indicia or patterns has no practical limitation, and can include dots, lines (e.g., straight or curved, formed from individual dots or continuously), a preselected pattern, or any combination thereof.

[0075] When patterning with the tip array in a level position, the indicia resulting from the disclosed methods have a high degree of sameness, and thus are uniform or substantially uniform in size, and preferably also in shape. The individual indicia feature size (e.g., a dot or line width) is highly uniform, for example within a tolerance of about 5%, or about 1%, or about 0.5%. The tolerance can be about 0.9%, about 0.8%, about 0.7%, about 0.6%, about 0.4%, about 0.3%, about 0.2%, or about 0.1%. Non-uniformity of feature size and/or shape can lead to roughness of indicia that can be undesirable for sub-micron type patterning.

[0076] As is known in the art, one capability of polymer pen arrays is the ability to print a gradient of feature sizes by tilting the tip array with respect to the pattern surface. The tip arrays in accordance with embodiments of the disclosure can similarly be used to expose a substrate and generate a gradient of feature sizes by tilting the tip array with respect to the pattern surface. For example, referring to Figure 3A, a tip array in accordance with embodiments of the disclosure was used such that each tip exposed an 8 x 6 array of points (7μιη pitch) for 2 seconds each on a substrate coating with a polymer bilayer of 100 nm photoresist atop 150 nm lift-office resist. The tilt of the tip array was chosen such that the tip-substrate distance varied by 6 μιη across the about 0.5 cm tip array. The tilt angle with respect to the surface to be patterned was about 0.07°. Various tip angles can be used as is known in the art for polymer pen arrays. Referring to Figure 3B, after developing the resists, evaporating 2 nm Cr and 10 nm Au, and removing the polymer using a chemical etch, Au features were obtained with a size gradient ranging from about 3 μιη to about 400 nm across the 0.5 cm sample. [0077] Referring to Figure 6, by utilizing thinner photoresist films and short exposure times, it was possible to generate isolated patterned featured as small as 250 nm + 30 nm. As also shown in Figure 6, continuous lines were also generated by writing dot patterns with pitches smaller than their feature size. In view of the versatility in pattern sizes, gradient feature sizes, and pattern shapes, the tip arrays in accordance with the disclosure can be used for a variety of micro- and nanofabrication tasks and combinatorial screening, such as screening of functional nanomaterials, soft matter, or biological processes.

[0078] The feature size can be about 10 nm to about 1 mm, about 10 nm to about 500 μιη, about 10 nm to about 100 μιη, about 50 nm to about 100 μιη, about 50 nm to about 50 μιη, about 50 nm to about 10 μιη, about 50 nm to about 5 μιη, or about 50 nm to about 1 μιη. Features sizes can be less than 1 μιη, less than about 900 nm, less than about 800 nm, less than about 700 nm, less than about 600 nm, less than about 500 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, less than about 100 nm, or less than about 90 nm.

System for Scanning Optical Lithography

[0079] A system for scanning optical lithography can include a radiation source for emitting a radiation in a path and a tip array as disclosed herein disposed in the path with the radiation being incident upon the tip substrate layer, such that the radiation is emitted through the tip ends of the tips. The system can further include a substrate stage disposed for selective contact with the tip array. The substrate stage can be, for example, a piezo stage. The tip array can optionally be operatively coupled to the radiation source and/or the substrate stage to perform a patterning method described herein. The apparatus can also include one or more spatial light modulators disposed in the radiation path between the radiation source and the tip array, for selective illumination of individual tips 14 in the array. For example, the system can include an array of spatial light modulators that are individually and dynamically controllable to selectively reflect the incident radiation or allow it to pass to the tip substrate layer and tip(s). The spatial light modulators can be coupled to the tip array 10. For example, the spatial light modulators can be disposed on the tip substrate layer 12 of the tip array 10.

EXAMPLES

Example 1: Method of Manufacturing a Tip Array

[0080] A tip array in accordance with embodiments of the disclosure was manufactured by preparing PDMS arrays of pyramids with 30 μιη base widths and 100 μιη pitch using previously published protocols. F. W. Huo, Z. J. Zheng, G. F. Zheng, L. R. Giam, H. Zhang, C. A. Mirkin, Science 2008, 321, 1658; D. J. Eichelsdoerfer, X. Liao, M. D. Cabezas, W. Morris, B. Radha, K. A. Brown, L. R. Giam, A. B. Braunschweig, C. A. Mirkin, Nat. Protoc. 2013, 8, 2548. In particular, vinyl-compound-rich prepolymer (VDT-731, Gelest) and hydro silane-rich crosslinker (HMS-301) were mixed in a weight ratio of 3.4: 1 and degassed. The mixture was poured onto a silicon master with recessed pyramidal microwells (30 μιη edge length, 100 μιη pitch) and cured at 80 °C overnight. The /z-PDMS pen array was peeled off and treated with 0₂ plasma at 150 mTorr and 45 W for 1 min.

[0081] Referring to Figures IB and 1C, the tip substrate layer was renderd opaque by coating the tip array, including the tips and the tip substrate layer, with 5 nm Ti and 200nm Au. This opaque layer of Ti and Au was coated by evarpoarting the Ti and Au onto the tip arary using an electron-beam evaporation systems (Kurt J. lesker Co., USA). A protective layer of poly(methyl methacrylate) (PMMA) (PMMA950 A3, MicroChem Inc., USA) was then coated on the Ti/Au layer disposed on the tip substrate layer. It was advantageously found that at specific PMMA concentrations and spin speeds, the PMMA coated the tip substrate layer, but not the tips themselves. The PMMA concentration can be in a range of 3% to 10% in anixole or chlorobenzene. The PMMA solution can be spin-coated at spin speeds of about 1000 to 3000 rpm. In the present example, the PMMA was spin-coated onto the tip substrate layer at 1000 rpm for 45 s followed by baking at 100°C for 10 min. The PMMA coating process was repeated once to ensure complete coverage. Chemical etching was then used to remove the Ti/Au layer on the tips. The tips were immersed in a gold etching solution (Gold Etchant TFA, Transense Company Inc., USA) for 70 seconds followed by titanium etching (Titanium Etchant TFT, Transense Company Inc., USA) for 5 seconds to remove the metal coatings on the tips while maintaining the portions of the tip substrate layer between the tips coated with the opaque Ti/Au coating.

Example 2: Lithography Procedure

[0082] An n-type <100> silicon wafer was spin-coated with a 450 nm thick layer of positive photoresist (Shipley 1805, MicroChem Inc., USA) at 4000 rpm for 45 seconds followed by soft-baking on a hot plate at 115°C for 1 min. For lift-off processing, a layer of lift-off resist (LOR 1A, MicroChem Inc., USA) was spin-coated at 4000 rpm for 45 s and then baked at 180 °C for 5 min. Subsequently, the pattern resist was spin-coated using a pre- diluted photoresist solution with propylene glycol monomethyl ether acetate (MicroChem Inc., USA) at 1: 1 v/v for 100 nm thick layers and 1:3 v/v for 40 nm thick layers. [0083] A tip array in accordance with the disclosure was mounted onto an apparatus and leveled to the photoresist-coated substrates optically. Patterns were generated under the control of piezoelectric actuators of a scanning probe platform (XE150, Park Systems) and a commercial digital micromirror device (DMD - DLP LightCommander, Logic PD) coupled with a collimated 440 mW 405 nm LED light source (M405L2, Thor Labs USA) to allow the exposure time between lsecond and 10 seconds.

[0084] After patterning, the photoresist was developed in MF24A (MicroChem Inc. USA) for 20 seconds to 30 seconds and rinsed with DI water. A layer of 2 nm Cr and 10 nm Au was evaporated onto the developed samples followed by etching of polymer resist in Remover PG (MicroChem Inc., USA) overnight. Patterns of photoresist and metals were characterized using optical microscopy (Axiovert-Zeiss), atomic force microscopy (Dimension Icon, Bruker), and scanning electron microscopy (S-4800-II, Hitachi).

Example 3: Photochemical Printing

[0085] The ink for photochemical patterning was prepared by mixing a fluorescent thiol (1 mg mL^"1), photoinitiator 2,2-dimethoxy-2-phenylacetophenone (0.3 mg mL^"1) and glycerol (50 mg mL^"1) in ethanol. Then the ink was spin coated onto the plasma-treated tip array (2000 rpm, 30 s). The piranha- washed Si wafers were immersed into the solution of 10-undecenyl trichlorosilane (1% v/v in toluene) for 2 hours to form the alkene-terminated surface. The inked tip array was mounted onto the scanning head, leveled and brought into contact with the alkene-modified substrate under simultaneous UV illumination (365 nm, 150-200 mW cm^" ) of the substrate through the tip array, with illumination time ranging from 1 minute to 4 minutes. After patterning, the substrate was sonicated in ethanol for 30 min and blow dried with nitrogen. Patterns were characterized using fluorescence microscopy

537-562 nm, m= 570-640 nm).

[0086] The foregoing describes and exemplifies the invention but is not intended to limit the invention defined by the claims which follow. All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the materials and methods of this invention have been described in terms of specific embodiments, it will be apparent to those of skill in the art that variations may be applied to the materials and/or methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved.

[0087] All patents, publications and references cited herein are hereby fully incorporated by reference. In case of conflict between the present disclosure and incorporated patents, publications and references, the present disclosure should control.

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Claims

What is Claimed:

1. A tip array comprising:

a tip substrate layer comprising a first surface and an oppositely disposed second surface; a plurality of tips fixed to the first surfaces, the tips comprising a tip end disposed opposite the first surface; and a blocking layer coated on the first surface, wherein the tip substrate layer is formed from a substrate material and the tips are formed from a tip material, the substrate material and the tip material each comprise an at least translucent material, the tips have a radius of curvature of less than about 1 μιη, and the tips are substantially free from the blocking layer.

2. The tip array of claim 1, wherein the tips are arranged in a regular periodic pattern.

3. The tip array of claim 1 or 2, wherein the tips are identically shaped.

4. The tip array of any one of the preceding claims, wherein the tips are pyramidal.

5. The tip array of any one of the preceding claims, wherein the tip substrate layer has a thickness of about 5 μιη to about 100 μιη.

6. The tip array of any one of the preceding claims, further comprising an at least translucent rigid support adhered to the second surface of the tip substrate layer.

7. The tip array of any one of the preceding claims, wherein the tip substrate layer and the tips have a combined thickness of less than about 1 mm.

8. The tip array of any one of the preceding claims, wherein the blocking layer is a metal.

9. The tip array of any one of the preceding claims, wherein the tip material and the substrate material are the same material.

10. The tip array of any one of claims 1 to 9, wherein the tip material is different than the substrate material, and the tip material does not extend past the first surface of the tip substrate layer.

11. The tip array of any one of the preceding claims, wherein one or both of the substrate material and the tip material comprise a polymer.

12. The tip array of any one of the preceding claims, wherein one or both of the substrate material and the tip material comprise a crosslinked polymer or a polymer gel.

13. The tip array of any one of the preceding claims, wherein one or both of the substrate material and the tip material comprise an elastomeric material.

14. The tip array of any one of the preceding claims, wherein one or both of the substrate material and the tip material are reversibly deformable.

15. The tip array of any one of the preceding claims, wherein one or both of the substrate material and the tip material comprise polydimethylsiloxane (PDMS).

16. The tip array of claim 15, wherein the PDMS comprises a trimethylsiloxy terminated vinylmethylsiloxane-dimethysiloxane copolymer, a methylhydrosiloxane- dimethylsiloxane copolymer, or a mixture thereof.

17. The tip array of any one of the preceding claims, wherein the plurality of tips are disposed with a tip-to-tip spacing in a range of about 1 μιη to about 10 mm.

18. The tip array of any one of the preceding claims, wherein each tip has a radius of curvature of less than about 0.2 μιη.

19. The tip array of any one of the preceding claims, wherein the tip substrate layer and tips comprise a polymer having a compression modulus of about 1 MPa to about 300 MPa.

20. The tip array of any one of the preceding claims, further comprising at least one spatial light modulator disposed on the tip substrate layer.

21. The tip array of claim 20, wherein the spatial light modulator is dynamically controllable.

22. The tip array of any one of the preceding claims, further comprising an array of spatial light modulators disposed on the tip substrate layer.

23. A method for sub-micron scale patterning, comprising:

coating a tip array of any one of the preceding claims with a patterning composition; contacting a substrate with the tip array to deliver the patterning composition to the substrate; and irradiating at least one tip of the tip array with a radiation source to transmit radiation through the tips and out the tip ends, thereby exposing the patterning composition and optionally the substrate to form at least one indicia on the substrate.

24. The method of claim 23, wherein the substrate is contacted with the tip array substantially simultaneously with irradiating at least one tip.

25. The method of claim 23 or 24, wherein the patterning composition is reactive to the radiation transmitted through the tip and out the tip end.

26. A method for sub-micron scale patterning, comprising:

contacting a photosensitive substrate with a tip array of any one of the preceding claims;

irradiating at least one tip of the tip array with a radiation source, to transmit radiation through the tip and out the tip end; and

exposing a portion of the photosensitive substrate with the transmitted radiation, thereby forming at least one indicia on the substrate.

27. The method of any one of claims 23 to 27, comprising irradiating all of the tips in the tip array.

28. The method of any one of claims 23 to 27, comprising selectively masking the second surface of the tip substrate layer to selectively illuminate at least one tip.

29. The method of any one of claims 23 to 28, further comprising moving the tip array, the substrate surface, or both after said contacting step and then repeating the contacting step.

30. The method of any one of claims 23 to 29, wherein the at least one indicia has a dot size (or line width) of less than 900 nm.

31. The method of any one of claims 23 to 30, wherein the at least one indicia has a dot size (or line width) of less than 100 nm.

32. The method of any one of claims 23 to 31, comprising irradiating with radiation having a wavelength in a range of 100 nm to 900 nm.

33. A method of making a tip array, comprising:

providing tip array comprising:

a tip substrate layer comprising a first surface and an oppositely disposed second surface, and a plurality of tips fixed to the first surface, the tips each comprising a tip end disposed opposite the first surface; and selectively coating a blocking layer on the first surface, wherein the tips remain substantially free of the blocking layer.

34. The method of claim 33, wherein selectively coating a blocking layer on the first surface comprises:

coating a blocking layer on the first surface and the tips, coating the blocking layer disposed on the first surface with a protective layer, wherein the blocking layer disposed on the tips remains exposed; selectively removing the exposed blocking layer; and removing the protective layer.

35. The method of claim 34, wherein the protective layer comprises PMMA.

36. The method of claim 34 or 35, wherein selectively removing the exposed blocking layer comprises etching the exposed blocking layer.

37. A system for beam pen lithography, comprising:

a radiation source for emitting a radiation in a path; a tip array of any one of claims 1 to 25 disposed in the radiation path such that the radiation, when active, is incident upon the tip substrate layer; and a substrate stage disposed for selective contacting of a substrate to the tip array.

38. The system of claim 37, wherein the substrate stage comprises a piezo stage.

39. The system of claim 37 or 38 further comprising at least one spatial light modulator disposed in the radiation path between the radiation source and the tip array.

40. The system of claim 39, further comprising an array of spatial light modulators disposed in the radiation path between the radiation source and the tip array.

41. The system of claim 39 or 40, wherein each spatial light modulator is individually controllable to selectively pass or reflect incident radiation from the radiation source.

42. The system of any one of claims 39 to 41 comprising a plurality of spatial light modulators, wherein the spatial light modulators are dynamically controllable.