Abstract
Here we disclose a lithographic pattern development process for amorphous fluoropolymers. Amorphous fluoropolymers are a class of plastic materials with high chemical inertness and favorable optical properties. Exposure of surface-deposited layers of such polymer with high energy radiation leads to a change in the chemical structure of the polymer, which selectively compromises the solubility of the exposed areas in fluorinated organic solvents. Micro- and nanopatterning with a feature size down to <50 nm was achieved by dissolving and removing unexposed amorphous fluoropolymer from exposed, surface deposited films. The amorphous fluoropolymer functions thus as a negative resist.
Claims
1. A method for the one-step chemical development of an amorphous fluoropolymer pattern on a solid substrate, which was prior obtained by exposing selected surface areas on the substrate to high energy radiation, comprising applying a developer, which is selected from a group comprising liquid fluorinated hydrocarbons, to the fluoropolymer film, so that only the exposed area of the amorphous fluoropolymer layer remains on the substrate, while the unexposed amorphous fluoropolymer is dissolved in the developer.
2. The method of claim 1 wherein the fluorinated hydrocarbon solvent is selected from the group consisting of perfluoro(2-butyltetrahydrofuran) (C8F16O), hexafluorobenzene (C6F6), perfluorodecalin (C10F18), 2H,3H-Decafluoropentane (C5H2F10), benzotrifluorde (C7H5F3), (trifluoromethyl)-, 1-butanamine, hexadecafluoroheptane (C7F16), Hexadecafluoro(1,3-dimethylcyclohexane).
Description
BRIEF DESCRIPTION OF DRAWINGS
(1) In the accompanying drawings:
(2) FIGS. 1A-1E show schematically top views of the substrate in the process of substrate preparation and surface patterning.
(3) FIG. 1A illustrates the top view of a clean solid substrate.
(4) FIG. 1B illustrates the top view of a clean solid substrate coated with a thin layer of a transparent conductive coating.
(5) FIG. 1C illustrates the top view of a solid substrate after coating with a thin layer of a transparent conductive coating and a thin layer of an amorphous fluoropolymer.
(6) FIG. 1D illustrates the top view of a coated substrate after exposure by high energy radiation, defining the pattern.
(7) FIG. 1E illustrates the side view of a coated and exposed substrate after development with developer.
(8) FIGS. 1F-1J show schematically side views of the substrate in the process of substrate preparation and surface patterning.
(9) FIG. 1F illustrates the side view of a clean solid substrate.
(10) FIG. 1G illustrates the side view of a clean solid substrate coated with a thin layer of a transparent conductive coating.
(11) FIG. 1H illustrates the side view of a solid substrate after coating with a thin layer of a transparent conductive coating and a thin layer of an amorphous fluoropolymer.
(12) FIG. 1I illustrates the side view of a coated substrate after exposure by high energy radiation, defining the pattern.
(13) FIG. 1J illustrates the side view of a coated and exposed substrate after development with developer.
(14) FIG. 2A illustrates schematically a set-up to deposit a thin layer of an amorphous fluoropolymer onto a solid substrate.
(15) FIG. 2B illustrates schematically a set-up to define the desired pattern on the fluoropolymer by exposing to a high energy radiation
(16) FIGS. 2C-2E are schematic representations showing possible methods of pattern development.
(17) FIG. 2C shows schematically pattern development by dipping of the exposed substrate into developer.
(18) FIG. 2D shows schematically pattern development by spraying the exposed substrate with developer.
(19) FIG. 2E shows schematically localized pattern development by means of a micropipette and a controlled flow of developer.
(20) FIG. 2F shows schematically a patterned substrate after development.
(21) FIG. 3A shows an optical microscopy image of a patterned amorphous fluoropolymer substrate after exposure by electron beam radiation.
(22) FIG. 3B shows an atomic force 2D micrograph of a patterned amorphous fluoropolymer substrate after exposure by electron beam radiation.
(23) FIG. 3C shows an atomic force 3D micrograph of a patterned amorphous fluoropolymer substrate after exposure by electron beam radiation.
(24) FIG. 4A shows an optical microscopy image of an e-beam exposed amorphous fluoropolymer-coated substrate after development.
(25) FIG. 4B shows an atomic force 2D micrograph of an e-beam exposed amorphous fluoropolymer-coated substrate after development.
(26) FIG. 4C shows atomic force 3D micrograph of an e-beam exposed amorphous fluoropolymer-coated substrate after development.
DESCRIPTION OF THE DRAWINGS
(27) FIG. 1 displays the process of substrate preparation, comprising spin coating of an amorphous fluoropolymer onto a solid substrate. For clarity both plane and profile views are presented. The clean solid substrate (0100) is coated with a thin layer of a transparent conductive coating (0101) and then a thin layer of an amorphous fluoropolymer (0102) is spun on top of the coating. The desired pattern is exposed by electron beam radiation (0103). After development all the unexposed areas is dissolved into the developer and only exposed areas are remained (0104).
(28) FIG. 2 provides an exemplary illustration of the set-up of the method. The coated solid substrate (0200) is placed on a spin-coater (0201) which rotates at a specific speed (0202). The amorphous fluoropolymer (0203) is put onto the substrate by a pipette (0204). The solid substrate covered by fluoropolymer (0205) is exposed by a high energy radiation (0207) producing the desired pattern (0206) at exposed areas. After exposure the substrate can be dipped into a container (0208) filled with the fluorinated hydrocarbon solvent as developer (0209), or the fluorinated hydrocarbon solvent can be sprayed (0210) by a nozzle (0211) placed above the exposed areas. The developer can also be applied by localized developing system including a micropipette (0212) and a controlled flow of developer (0213). After development, all the unexposed fluoropolymer is dissolved by the developer and only the exposed fluoropolymer (2014) is remained on the surfaces, surrounding by transparent conductive coating (2015).
(29) FIG. 3 shows optical microscopic image (FIG. 3A) and atomic force 2D and 3D macrographs (FIG. 3B and FIG. 3C) of a patterned amorphous fluoropolymer exposed by electron beam radiation. An amorphous fluoropolymer is spun onto a solid substrate (0300) and desired pattern is exposed by e-beam radiation (0301). Gold alignment marks (0302) are used to find the structure easier.
(30) FIG. 4 shows optical microscopic image (FIG. 3A) and atomic force 2D and 3D macrographs (FIG. 3B and FIG. 3C) of e-beam exposed amorphous fluoropolymer after development by fluorinated hydrocarbon developer. After development only exposed areas of amorphous fluoropolymer (0401) remain on the transparent conductive coating (0400) while the rest of unexposed fluoropolymer is removed by the developer. Gold alignment marks (0402) are used to find the structure easier.
DETAILED DESCRIPTION
(31) The embodiments of this method provide means for the generation of amorphous fluoropolymer patterns on solid surfaces, featuring high resolution with feature sizes ranging from the micrometer to the low nanometer size scale.
(32) First a solid surface (0100) is selected and cleaned (FIG. 1). In one aspect the solid substrate is transparent. In a preferred embodiment the transparent solid substrate is glass. In other embodiments the transparent solid substrate is quartz, mica or polymer. In another aspect the solid substrate is opaque including metal, semiconductor amorphous materials and ceramics. Second, the solid substrate can be coated with a thin layer of a conductive coating (0101). In one aspect the transparent conductive coating is an oxide. In a preferred embodiment the transparent coating is indium tin oxide (ITO). In other embodiments the transparent oxide is indium doped cadmium oxide (ICO), aluminum doped zinc oxide (ZnO:Al), gallium doped zinc Oxide (ZnO:Ga), indium doped zinc oxide (IZO) or zinc oxide (ZnO). In other aspects the conductive coating is graphene, carbon nanofiber, polymer or metal. Third, a thin layer of an amorphous fluoropolymer (0203) is deposited on the solid substrate coated with a thin conductive film (0200). In one aspect the amorphous fluoropolymer is Teflon AF 1600. In another aspect the amorphous fluoropolymer is Teflon AF 2400. In a preferred embodiment thin layer of the amorphous fluoropolymer is generated by spin-coating (FIG. 2A). In other embodiments the thin layer of amorphous fluoropolymer is generated by meniscus coating, capillary coating, extrusion coating, extrude-and-spin coating and patch coating. In a preferred embodiment the thickness of the amorphous fluoropolymer is 500 nm. In other embodiments the thickness of the amorphous fluoropolymer is in the range of 10 nm to 500 μm. Fourth, the substrate coated with amorphous fluoropolymer (0205) is exposed by a high energy radiation (0207) producing the desired pattern at exposed areas (0206) (FIG. 2B). In a preferred embodiment the high energy radiation is an electron beam, which is common equipment in most fabrication facilities. In other embodiments the high energy radiation is an X-ray beam, synchrotron radiation, laser radiation, or a focused ion beam. Finally, the exposed amorphous fluoropolymer film is developed with a fluorinated hydrocarbon solvent (0209). In a preferred embodiment the fluorinated hydrocarbon solvent is perfluoro (2-butyltetrahydrofuran), but the developer can comprise a variety of other perfluorinated solvents, including perfluoro-2-butyltetrahydrofuran (C.sub.8F.sub.16O), hexafluorobenzene (C.sub.6F.sub.6), perfluorodecalin (C.sub.10F.sub.18), 2H,3H-Decafluoropentane (C.sub.5H.sub.2F.sub.10), benzotrifluorde (C.sub.7H.sub.5F.sub.3), (trifluoromethyl)-, 1-butanamine, hexadecafluoroheptane (C.sub.7F.sub.16), Hexadecafluoro(1,3-dimethylcyclohexane), perfluoro-1,3-dimethylcyclohexane (C.sub.8F.sub.16), 2H,3H-Decafluoropentane octafluorotoluene (C.sub.7F.sub.8) and is perfluorooctyl bromide (C.sub.8BrF.sub.17). In another aspect the developer is a mixture of fluorinated hydrocarbon solvents in order to regulate the duration of the development process. Such a mixture can comprise, for example, perfluorononane and perfluoro-2-butyltetrahydrofuran (C.sub.8F.sub.16O) in a 1:1 (v/v) mixture. The exposed fluoropolymer coated substrates are brought in contact with the developer, until the exposed pattern is liberated from the amorphous fluoropolymer film. In a preferred embodiment the exposed surface is immersed, or dipped into fluorinated hydrocarbon solvent (FIG. 2C). In other embodiments the developer can be applied by spraying (FIG. 2D), or locally on selected substrate surface areas by a microflow needle or microfluidic device (FIG. 2E). During development, unexposed amorphous fluoropolymer is dissolved in the fluorinated hydrocarbon solvent, such that only the exposed areas (2015) remain on the substrate after development (FIG. 2F). Development can be controlled by adjusting development parameters. In one aspect, the temperature is regulated. Temperature can be increased to increase the solubility of the unexposed fluoropolymer in the developer. In another aspect, the developing time is regulated. For each amorphous fluoropolymer, an optimal development time has to be determined, in order to avoid over- or underdevelopment. In yet another aspect the substrate carrying the exposed amorphous fluoropolymer film is either held still, or is agitated, or is sonicated, in order to improve the contact between the developer liquid and the amorphous fluoropolymer film, and to facilitate the removal of dissolved material from the surface. After the development is complete, the substrates are washed, dried and characterized according to common fabrication procedures.
Example
(33) A non-limiting example of the invention is presented herein. FIG. 3 shows a thin layer of Teflon AF 1600 after exposure by e-beam radiation. The desired pattern on 500 nm thick Teflon AF 1600 film is exposed by 100 keV accelerated electron beam radiation with a 500-1500 μC/cm.sup.2 dose range. In FIG. 3A, a micrograph of an exposed Teflon film on a ITO/glass substrate is displayed. Exposed areas are visible, due to the structural change in the exposed Teflon AF (0301), it can be distinguished from the unexposed Teflon AF (0300). Alignment marks (0302) help to locate the exposed regions. FIG. 3B is an AFM topography image of a locally exposed Teflon AF film. The unexposed areas (0300) appear bright, the exposed areas (0301) appear dark. The brightness encodes the absolute hight, showing a hight difference in the nanometer range between exposed and unexposed Teflon AF. After a 2 minute development at 20° C., subsequent to exposure, by means of perfluoro (2-buthyltetrahydrofuran), the e-beam exposed Teflon remains on the substrate while the unexposed Teflon has been removed by the developer solvent. FIG. 4A is a micrograph of the exposed, and subsequently developed Teflon film on a ITO/glass substrate. Exposed areas (0401) are visible as brighter areas, due to removed unexposed Teflon AF, easily distinguished from the uncoated substrate (0400). Alignment marks (0402) facilitate locating the exposed and developed pattern. FIG. 4B is a AFM 2D-topography image, and FIG. 4C a AFM 3D-topography image of an exposed and developed Teflon AF pattern. The developed pattern (0401) appears bright, and the substrate areas (0400) appear dark. The gap between the two exposed areas is ˜50 nm wide.
(34) Materials
(35) Substrate:
(36) Unbeveled, CNC (Computer Numerical Control) precision cut, thin borosilicate glass substrate (diameter: 50 mm (+/−0.25)×50 mm (+/−0.25); thickness: 0.175 mm (+/−0.015)) coated with ITO-coating (20+/−5 Ohms/sq.) with no SiO.sub.2 layer from Präzisions Glas & Optik (Iserlohn, Germany)
(37) Chemicals:
(38) Teflon AF solution grade 601S2-100-6 1600 (6% (w/w) solids contents, based on Teflon AF1600, glass transition temperature Tg=160° C.) from Dupont Chemicals (Wilmington, US); HMDS (Hexamethyldisiloxane) from Micro Resist Technology GmbH (Berlin, Germany); Perfluoro (2-buthyltetrahydrofuran) from Tokyo Chemical Industry (Tokyo, Japan); Fluorinert FC-770 (CAS Number 86508-42-1) from Sigma Aldrich (Missouri, USA).
(39) Equipment:
(40) The Electron Beam Lithography system EBL-JEOL JBX-9300FS, from JEOL, Tokyo, Japan was used as radiation source for exposure. Electron Beam Evaporator (AVAC-HVC600) was used for the deposition of alignment marks. Dry plasma etching system (BatchTop PE/RIE m/95, PlasmaTherm/Advanced Vacuum, USA, was used for pre-treatment of the substrates. Standard clean-room fabrication methods and equipment was used for common substrate preparation steps.
(41) Microscopy:
(42) Scanning Electron microscope (Leo Ultra 55 FEG, Zeiss); AFM images were recorded using a Veeco Dimension 3100 SPM scanning probe microscope in tapping mode with a NSG01 DLC probe (NT-MDT Europe BV, Netherlands), The transmission optical micrographs were recorded using an Olympus reflected light optical microscope, with a LMPLFL50XBD objective, and a SONY ST50CCD Video camera.
(43) Process
(44) The ITO substrate was cleaned by spraying with acetone and subsequently isopropanol. To remove all the possible organic contaminants, the substrate was plasma treated (10 sccm oxygen, 500 mbar, 50 W) for 10 min. HMDS (Hexamethyldisiloxane) was spin-coated onto the substrate (3000 rpm) and baked on a hot plate (110° C. for 90 s) to improve the adhesion of Teflon to the substrate. Teflon AF 1600 (0203) was spin-coated (0202) onto the substrate (2000 rpm) and baked for 15 min at 180° C. beyond the glass transition temperature of Teflon AF. The substrate was then loaded into an electron beam lithography system (EBL-JEOL JBX-9300FS) where it was exposed by electron beam radiation (0207) using a pre-designed pattern. After exposure, the substrate was immersed in perfluoro (2-butyl tetrahydrofuran) (0209) in a glass container (0208). The unexposed surface area dissolved in the developer solvent, while the exposed pattern (0206) remained on the surface. After 2 min of development, the substrate was removed from the developer bath, washed with FC770, and dried by air blowing. The surfaces are stored under nitrogen.
REFERENCES
(45) 1. Amorphous fluoropolymers—A new generation of products. Korinek, p. M. 1994, Macromolecular symposia, pp. 61-65. 2. Micro- and Nano-Scale Fabrication of Fluorinated Polymers by Direct Etching Using Focused Ion Beam. Fukutake, N., et al. s.l.: Japanese Journal of Applied Physics, 2010, Vol. 49. 3. Direct Electron-Beam Patterning of Teflon AF. Karre, V., et al. 2, s.l.: Transactions on Nanotechnology, 2009, Vol. 8. 4. Nano- and micro-fabrication of perfluorinated polymers using quantum beam technology. Miyoshi, N., et al. s.l.: Radiation Physics and Chemistry, 2011, Vol. 80. 230-235.
